Birth cohort relative to an influenza A virus's antigenic cluster introduction drives patterns of children's antibody titers.

An individual's antibody titers to influenza A strains are a result of the complicated interplay between infection history, cross-reactivity, immune waning, and other factors. It has been challenging to disentangle how population-level patterns of humoral immunity change as a function of age, calendar year, and birth cohort from cross-sectional data alone. We analyzed 1,589 longitudinal sera samples from 260 children across three studies in Nicaragua, 2006-16. Hemagglutination inhibition (HAI) titers were determined against four H3N2 strains, one H1N1 strain, and two H1N1pdm strains. We assessed temporal patterns of HAI titers using an age-period-cohort modeling framework. We found that titers against a given virus depended on calendar year of serum collection and birth cohort but not on age. Titer cohort patterns were better described by participants' ages relative to year of likely introduction of the virus's antigenic cluster than by age relative to year of strain introduction or by year of birth. These cohort effects may be driven by a decreasing likelihood of early-life infection after cluster introduction and by more broadly reactive antibodies at a young age. H3N2 and H1N1 viruses had qualitatively distinct cohort patterns, with cohort patterns of titers to specific H3N2 strains reaching their peak in children born 3 years prior to that virus's antigenic cluster introduction and with titers to H1N1 and H1N1pdm strains peaking for children born 1-2 years prior to cluster introduction but not being dramatically lower for older children. Ultimately, specific patterns of strain circulation and antigenic cluster introduction may drive population-level antibody titer patterns in children.

The Nicaraguan Pediatric Influenza Cohort Study, 2011-2019: Influenza Incidence, Seasonality, and Transmission.

BACKGROUND: Children account for a large portion of global influenza burden and transmission, and a better understanding of influenza in children is needed to improve prevention and control strategies. METHODS: To examine the incidence and transmission of influenza we conducted a prospective community-based study of children aged 0-14 years in Managua, Nicaragua, between 2011 and 2019. Participants were provided with medical care through study physicians and symptomatic influenza was confirmed by reverse-transcription polymerase chain reaction (RT-PCR). Wavelet analyses were used to examine seasonality. Generalized growth models (GGMs) were used to estimate effective reproduction numbers. RESULTS: From 2011 to 2019, 3016 children participated, with an average of ∼1800 participants per year and median follow-up time of 5 years per child, and 48.3% of the cohort in 2019 had been enrolled their entire lives. The overall incidence rates per 100 person-years were 14.5 symptomatic influenza cases (95% confidence interval [CI]: 13.9-15.1) and 1.0 influenza-associated acute lower respiratory infection (ALRI) case (95% CI: .8-1.1). Symptomatic influenza incidence peaked at age 9-11 months. Infants born during peak influenza circulation had lower incidence in the first year of their lives. The mean effective reproduction number was 1.2 (range 1.02-1.49), and we observed significant annual patterns for influenza and influenza A, and a 2.5-year period for influenza B. CONCLUSIONS: This study provides important information for understanding influenza epidemiology and informing influenza vaccine policy. These results will aid in informing strategies to reduce the burden of influenza.

Rapid Epidemic Expansion of Chikungunya Virus East/Central/South African Lineage, Paraguay.

The spread of Chikungunya virus is a major public health concern in the Americas. There were >120,000 cases and 51 deaths in 2023, of which 46 occurred in Paraguay. Using a suite of genomic, phylodynamic, and epidemiologic techniques, we characterized the ongoing large chikungunya epidemic in Paraguay.

Surveillance for variants of SARS-CoV-2 to inform risk assessments.

Since the beginning of the coronavirus disease 2019 (COVID-19) pandemic, numerous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants have emerged, some leading to large increases in infections, hospitalizations and deaths globally. The virus's impact on public health depends on many factors, including the emergence of new viral variants and their global spread. Consequently, the early detection and surveillance of variants and characterization of their clinical effects are vital for assessing their health risk. The unprecedented capacity for viral genomic sequencing and data sharing built globally during the pandemic has enabled new variants to be rapidly detected and assessed. This article describes the main variants circulating globally between January 2020 and June 2023, the genetic features driving variant evolution, and the epidemiological impact of these variants across countries and regions. Second, we report how integrating genetic variant surveillance with epidemiological data and event-based surveillance, through a network of World Health Organization partners, supported risk assessment and helped provide guidance on pandemic responses. In addition, given the evolutionary characteristics of circulating variants and the immune status of populations, we propose future directions for the sustainable genomic surveillance of SARS-CoV-2 variants, both nationally and internationally: (i) optimizing variant surveillance by including environmental monitoring; (ii) coordinating laboratory assessment of variant evolution and phenotype; (iii) linking data on circulating variants with clinical data; and (iv) expanding genomic surveillance to additional pathogens. Experience during the COVID-19 pandemic has shown that genomic surveillance of pathogens can provide essential, timely and evidence-based information for public health decision-making.

Depuis le début de la pandémie de coronavirus survenue en 2019 (COVID-19), de nombreux variants du coronavirus 2 du syndrome respiratoire aigu sévère (SARS-CoV-2) sont apparus, certains entraînant une forte augmentation du nombre d'infections, d'hospitalisations et de décès dans le monde. L'impact du virus sur la santé publique dépend de nombreux facteurs, notamment l'émergence de nouveaux variants viraux et leur propagation à l'échelle mondiale. Par conséquent, la détection précoce et la surveillance des variants ainsi que la caractérisation de leurs effets cliniques sont essentielles pour évaluer leur risque pour la santé. La capacité sans précédent de séquençage du génome viral et de partage des données, capacité mise en place à l'échelle mondiale pendant la pandémie, a permis de détecter et d'évaluer rapidement de nouveaux variants. Le présent article décrit les principaux variants circulant dans le monde entre janvier 2020 et juin 2023, les caractéristiques génétiques à l'origine de leur évolution et leur impact épidémiologique dans les différents pays et régions. Ensuite, nous expliquerons comment l'intégration de la surveillance des variants génétiques aux données épidémiologiques et à la surveillance fondée sur les événements, par l'intermédiaire d'un réseau de partenaires de l'Organisation mondiale de la santé, a permis de faciliter l'évaluation des risques et de fournir des orientations sur les mesures à prendre en période de pandémie. En outre, compte tenu des caractéristiques évolutives des variants en circulation et de l'état immunitaire des populations, nous proposons des orientations futures pour une surveillance génomique durable des variants du SARS-CoV-2, au niveau tant national qu'international: (i) optimiser la surveillance des variants en incluant le suivi environnemental; (ii) coordonner l'évaluation en laboratoire de l'évolution des variants et du phénotype; (iii) établir un lien entre les données sur les variants en circulation et les données cliniques; et (iv) étendre la surveillance génomique à d'autres agents pathogènes. L'expérience de la pandémie de COVID-19 a mis en évidence que la surveillance génomique des agents pathogènes peut fournir en temps utile des informations essentielles fondées sur des preuves en vue de la prise de décisions en matière de santé publique.

Desde el inicio de la pandemia de la enfermedad por coronavirus de 2019 (COVID-19), han aparecido numerosas variantes del coronavirus de tipo 2 causante del síndrome respiratorio agudo severo (SRAS-CoV-2), algunas de las que han provocado un gran aumento de las infecciones, hospitalizaciones y muertes en todo el mundo. El impacto del virus en la salud pública depende de muchos factores, entre ellos la aparición de nuevas variantes víricas y su propagación mundial. En consecuencia, la detección y vigilancia tempranas de las variantes y la caracterización de sus efectos clínicos son vitales para evaluar su riesgo sanitario. La capacidad sin precedentes de secuenciación genómica viral y de intercambio de datos creada a nivel mundial durante la pandemia ha permitido detectar y evaluar rápidamente variantes nuevas. En este artículo se describen las principales variantes que circulan a nivel mundial entre enero de 2020 y junio de 2023, la característica genética que impulsa la evolución de las variantes y el impacto epidemiológico de estas variantes en los diferentes países y regiones. En segundo lugar, se informa de cómo la integración de la vigilancia de variantes genéticas con los datos epidemiológicos y la vigilancia basada en eventos, a través de una red de asociados de la Organización Mundial de la Salud, apoyó la evaluación de riesgos y ayudó a proporcionar orientación sobre las respuestas a la pandemia. Además, dadas las características evolutivas de las variantes circulantes y el estado inmunitario de las poblaciones, se proponen orientaciones futuras para la vigilancia genómica sostenible de las variantes del SRAS-CoV-2, tanto a nivel nacional como internacional: (i) optimizar la vigilancia de las variantes mediante la inclusión de la monitorización ambiental; (ii) coordinar la evaluación de laboratorio de la evolución y el fenotipo de las variantes; (iii) vincular los datos sobre las variantes circulantes con los datos clínicos; y (iv) ampliar la vigilancia genómica a patógenos adicionales. La experiencia durante la pandemia de la COVID-19 ha demostrado que la vigilancia genómica de patógenos puede proporcionar información esencial, oportuna y basada en evidencias para la toma de decisiones en materia de salud pública.

Viral reactivations and co-infections in COVID-19 patients: a systematic review.

BACKGROUND: Viral reactivations and co-infections have been reported among COVID-19 patients. However, studies on the clinical outcomes of different viral reactivations and co-infections are currently in limit. Thus, the primary purpose of this review is to perform an overarching investigation on the cases of latent virus reactivation and co-infection in COVID-19 patients to build collective evidence contributing to improving patient health. The aim of the study was to conduct a literature review to compare the patient characteristics and outcomes of reactivations and co-infections of different viruses. METHODS: Our population of interest included confirmed COVID-19 patients who were diagnosed with a viral infection either concurrently or following their COVID-19 diagnosis. We extracted the relevant literature through a systematic search using the key terms in the online databases including the EMBASE, MEDLINE, Latin American Caribbean Health Sciences Literature (LILACS), from inception onwards up to June 2022. The authors independently extracted data from eligible studies and assessed the risk of bias using the Consensus-based Clinical Case Reporting (CARE) guidelines and the Newcastle-Ottawa Scale (NOS). Main patient characteristics, frequency of each manifestation, and diagnostic criteria used in studies were summarized in tables. RESULTS: In total, 53 articles were included in this review. We identified 40 reactivation studies, 8 coinfection studies, and 5 studies where concomitant infection in COVID-19 patients was not distinguished as either reactivation or coinfection. Data were extracted for 12 viruses including IAV, IBV, EBV, CMV, VZV, HHV-1, HHV-2, HHV-6, HHV-7, HHV-8, HBV, and Parvovirus B19. EBV, HHV-1, and CMV were most frequently observed within the reactivation cohort, whereas IAV and EBV within the coinfection cohort. In both reactivation and coinfection groups, patients reported cardiovascular disease, diabetes, and immunosuppression as comorbidities, acute kidney injury as complication, and lymphopenia and elevated D-dimer and CRP levels from blood tests. Common pharmaceutical interventions in two groups included steroids and antivirals. CONCLUSION: Overall, these findings expand our knowledge on the characteristics of COVID-19 patients with viral reactivations and co-infections. Our experience with current review indicates a need for further investigations on virus reactivation and coinfection among COVID-19 patients.

Single-Dose Vaccination Among Infants and Toddlers Provides Modest Protection Against Influenza Illness, Which Wanes After 5 Months.

In their first season of vaccination, young children are recommended 2 doses of influenza vaccine, but a 2-dose schedule might be difficult to implement in many countries. Within a cohort study of 742 children aged 6 to <24 months in Managua, Nicaragua, this study estimated effectiveness of partial vaccination from 3 to 9 months postvaccination. Vaccine effectiveness was 74% (95% confidence interval [CI], 24%-91%) within 3 months and 55% (95% CI, 10%-77%) within 4 months. There was not significant protection beyond 5 months. Partial vaccination might confer some benefits but should be followed by a second dose.

Pneumonia Following Symptomatic Influenza Infection Among Nicaraguan Children Before and After Introduction of the Pneumococcal Conjugate Vaccine.

Influenza is associated with primary viral and secondary bacterial pneumonias; however, the dynamics of this relationship in populations with varied levels of pneumococcal vaccination remain unclear. We conducted nested matched case-control studies in 2 prospective cohorts of Nicaraguan children aged 2-14 years: 1 before pneumococcal conjugate vaccine introduction (2008-2010) and 1 following introduction and near universal adoption (2011-2018). The association between influenza and pneumonia was similar in both cohorts. Participants with influenza (across types/subtypes) had higher odds of developing pneumonia in the month following influenza infection. These findings underscore the importance of considering influenza in interventions to reduce global pneumonia burden.

Obesity Is Associated With Increased Susceptibility to Influenza A (H1N1pdm) but Not H3N2 Infection.

BACKGROUND: Obesity has been shown to increase the risk of severe outcomes and death for influenza virus infections. However, we do not understand the influence of obesity on susceptibility to infection or on nonsevere influenza outcomes. METHODS: We performed a case-ascertained, community-based study of influenza transmission within households in Nicaragua. To investigate whether obesity increases the likelihood of influenza infection and symptomatic infection we used logistic regression models. RESULTS: Between 2015 and 2018, a total of 335 index cases with influenza A and 1506 of their household contacts were enrolled. Obesity was associated with increased susceptibility to symptomatic H1N1pdm infection among adults (odds ratio [OR], 2.10; 95% confidence interval [CI], 1.08-4.06) but not children, and this association increased with age. Among adults with H1N1pdm infection, obesity was associated with increased likelihood of symptoms (OR, 3.91; 95% CI, 1.55-9.87). For middle-aged and older adults with obesity there was also a slight increase in susceptibility to any H1N1pdm infection (OR, 1.20; 95% CI, .62-2.34). Body mass index (BMI) was also linearly associated with increased susceptibility to symptomatic H1N1pdm infection, primarily among middle-aged and older women (5-unit BMI increase OR, 1.40; 95% CI, 1.00-1.97). Obesity was not associated with increased H3N2 susceptibility or associated symptoms. CONCLUSIONS: We found that, among adults, obesity is associated with susceptibility to H1N1pdm infection and with symptoms associated with H1N1pdm infection, but not with susceptibility to H3N2 infection or associated symptoms. These findings will help target prevention efforts and therapeutics to this high-risk population.

Individual-level Association of Influenza Infection With Subsequent Pneumonia: A Case-control and Prospective Cohort Study.

BACKGROUND: Pneumonia is a leading cause of mortality worldwide. Influenza may result in primary pneumonia or be associated with secondary bacterial pneumonia. While the association with secondary pneumonia has been established ecologically, individual-level evidence remains sparse and the risk period for pneumonia following influenza poorly defined. METHODS: We conducted a matched case-control study and a prospective cohort study among Nicaraguan children aged 0-14 years from 2011 through 2018. Physicians diagnosed pneumonia cases based on Integrated Management for Childhood Illness guidelines. Cases were matched with up to 4 controls on age (months) and study week. We fit conditional logistic regression models to assess the association between influenza subtype and subsequent pneumonia development, and a Bayesian nonlinear survival model to estimate pneumonia hazard following influenza. RESULTS: Participants with influenza had greater risk of developing pneumonia in the 30 days following onset compared to those without influenza (matched odds ratio [mOR], 2.7 [95% confidence interval {CI}, 1.9-3.9]). Odds of developing pneumonia were highest for participants following A(H1N1)pdm09 illness (mOR, 3.7 [95% CI, 2.0-6.9]), followed by influenza B and A(H3N2). Participants' odds of pneumonia following influenza were not constant, showing distinct peaks 0-6 days (mOR, 8.3 [95% CI, 4.8-14.5] days) and 14-20 (mOR, 2.5 [95% CI, 1.1-5.5] days) after influenza infection. CONCLUSIONS: Influenza is a significant driver of both primary and secondary pneumonia among children. The presence of distinct periods of elevated pneumonia risk in the 30 days following influenza supports multiple etiological pathways.

Dynamics and determinants of the force of infection of dengue virus from 1994 to 2015 in Managua, Nicaragua.

Dengue virus (DENV) is the most prevalent human vector-borne viral disease. The force of infection (FoI), the rate at which susceptible individuals are infected in a population, is an important metric for infectious disease modeling. Understanding how and why the FoI of DENV changes over time is critical for developing immunization and vector control policies. We used age-stratified seroprevalence data from 12 years of the Pediatric Dengue Cohort Study in Nicaragua to estimate the annual FoI of DENV from 1994 to 2015. Seroprevalence data revealed a change in the rate at which children acquire DENV-specific immunity: in 2004, 50% of children age >4 years were seropositive, but by 2015, 50% seropositivity was reached only by age 11 years. We estimated a spike in the FoI in 1997-1998 and 1998-1999 and a gradual decline thereafter, and children age <4 years experienced a lower FoI. Two hypotheses to explain the change in the FoI were tested: (i) a transition from introduction of specific DENV serotypes to their endemic transmission and (ii) a population demographic transition due to declining birth rates and increasing life expectancy. We used mathematical models to simulate these hypotheses. We show that the initial high FoI can be explained by the introduction of DENV-3 in 1994-1998, and that the overall gradual decline in the FoI can be attributed to demographic shifts. Changes in immunity and demographics strongly impacted DENV transmission in Nicaragua. Population-level measures of transmission intensity are dynamic and thus challenging to use to guide vaccine implementation locally and globally.

Assessing the Incidence of Symptomatic Respiratory Syncytial Virus Illness Within a Prospective Birth Cohort in Managua, Nicaragua.

BACKGROUND: Respiratory syncytial virus (RSV) causes substantial morbidity and mortality among children worldwide, commonly through acute lower respiratory tract infections (ALRI). To assess the incidence rate of symptomatic RSV illness among young children, we conducted a prospective birth cohort study following children from 0-2 years of age in Managua, Nicaragua. METHODS: Children meeting the testing criteria (fever, history of fever, or severe respiratory symptoms [apnea, stridor, nasal flaring, wheezing, chest indrawing, and/or central cyanosis]) were tested for RSV infections using real-time reverse transcriptase-polymerase chain reaction. An acute lower respiratory infection was defined as a diagnosis of pneumonia, bronchiolitis, bronchitis, or bronchial hyperreactivity. The incidence rate was calculated, and 95% confidence intervals were estimated using a Poisson distribution. RESULTS: A total of 833 children participated in the cohort: 289 (34.7%) had at least 1 episode of laboratory-confirmed RSV, and 156 (18.7%) of had an episode of RSV-associated ALRI (RSV-ALRI). The incidence rate of symptomatic RSV was 248.1 cases per 1000 person-years (95% confidence interval [CI] 223.2-275.7). While infants aged 6-11 months had the highest incidence of symptomatic RSV (361.3/1000 person-years, 95% CI 304.4-428.8), infants <3 months had the highest incidence of severe RSV (RSV-associated hospitalizations and/or severe ALRI). RSV was also associated with 25.0-37.5% of deaths from medical causes (n = 8). CONCLUSIONS: A substantial burden of RSV exists among children aged <2 years in Nicaraguan communities. RSV was also a leading cause of infant mortality among study participants. The development and implementation of effective RSV prevention and treatment measures represent an opportunity to substantially reduce severe illness and death among children worldwide.

Association Between the Respiratory Microbiome and Susceptibility to Influenza Virus Infection.

BACKGROUND: Previous studies suggest that the nose/throat microbiome may play an important role in shaping host immunity and modifying the risk of respiratory infection. Our aim is to quantify the association between the nose/throat microbiome and susceptibility to influenza virus infection. METHODS: In this household transmission study, index cases with confirmed influenza virus infection and their household contacts were followed for 9-12 days to identify secondary influenza infections. Respiratory swabs were collected at enrollment to identify and quantify bacterial species via high-performance sequencing. Data were analyzed by an individual hazard-based transmission model that was adjusted for age, vaccination, and household size. RESULTS: We recruited 115 index cases with influenza A(H3N2) or B infection and 436 household contacts. We estimated that a 10-fold increase in the abundance in Streptococcus spp. and Prevotella salivae was associated with 48% (95% credible interval [CrI], 9-69%) and 25% (95% CrI, 0.5-42%) lower susceptibility to influenza A(H3N2) infection, respectively. In contrast, for influenza B infection, a 10-fold increase in the abundance in Streptococcus vestibularis and Prevotella spp. was associated with 63% (95% CrI, 17-83%) lower and 83% (95% CrI, 15-210%) higher susceptibility, respectively. CONCLUSIONS: Susceptibility to influenza infection is associated with the nose/throat microbiome at the time of exposure. The effects of oligotypes on susceptibility differ between influenza A(H3N2) and B viruses. Our results suggest that microbiome may be a useful predictor of susceptibility, with the implication that microbiome could be modulated to reduce influenza infection risk, should these associations be causal.

Pre-existing Antineuraminidase Antibodies Are Associated With Shortened Duration of Influenza A(H1N1)pdm Virus Shedding and Illness in Naturally Infected Adults.

BACKGROUND: Influenza causes a substantial burden worldwide, and current seasonal influenza vaccine has suboptimal effectiveness. To develop better, more broadly protective vaccines, a more thorough understanding is needed of how antibodies that target the influenza virus surface antigens, hemagglutinin (HA) (including head and stalk regions) and neuraminidase (NA), impact influenza illness and virus transmission. METHODS: We used a case-ascertained, community-based study of household influenza virus transmission set in Managua, Nicaragua. Using data from 170 reverse transcriptase-polymerase chain reaction (RT-PCR)-confirmed influenza virus A(H1N1)pdm infections and 45 household members with serologically confirmed infection, we examined the association of pre-existing NA, hemagglutination inhibiting, and HA stalk antibody levels and influenza viral shedding and disease duration using accelerated failure time models. RESULTS: Among RT-PCR-confirmed infections in adults, pre-existing anti-NA antibody levels ≥40 were associated with a 69% (95% confidence interval [CI], 34-85%) shortened shedding duration (mean, 1.0 vs 3.2 days). Neuraminidase antibody levels ≥80 were associated with further shortened shedding and significantly shortened symptom duration (influenza-like illness, 82%; 95% CI, 39-95%). Among RT-PCR-confirmed infections in children, hemagglutination inhibition titers ≥1:20 were associated with a 32% (95% CI, 13-47%) shortened shedding duration (mean, 3.9 vs 6.0 days). CONCLUSIONS: Our results suggest that anti-NA antibodies play a large role in reducing influenza illness duration in adults and may impact transmission, most clearly among adults. Neuraminidase should be considered as an additional target in next-generation influenza virus vaccine development.We found that antibodies against neuraminidase were associated with significantly shortened viral shedding, and among adults they were also associated with shortened symptom duration. These results support neuraminidase as a potential target of next-generation influenza virus vaccines.

Epidemiological Evidence for Lineage-Specific Differences in the Risk of Inapparent Chikungunya Virus Infection.

In late 2013, chikungunya virus (CHIKV) was introduced into the Americas, leading to widespread epidemics. A large epidemic caused by the Asian chikungunya virus (CHIKV) lineage occurred in Managua, Nicaragua, in 2015. Literature reviews commonly state that the proportion of inapparent CHIKV infections ranges from 3 to 28%. This study estimates the ratio of symptomatic to asymptomatic CHIKV infections and identifies risk factors of infection. In October to November 2015, 60 symptomatic CHIKV-infected children were enrolled as index cases and prospectively monitored, alongside 236 household contacts, in an index cluster study. Samples were collected upon enrollment and on day 14 or 35 and tested by real-time reverse transcription-PCR (rRT-PCR), IgM capture enzyme-linked immunosorbent assays (IgM-ELISAs), and inhibition ELISAs to detect pre- and postenrollment CHIKV infections. Of 236 household contacts, 55 (23%) had experienced previous or very recent infections, 41 (17%) had active infections at enrollment, and 21 (9%) experienced incident infections. Vehicle ownership (multivariable-adjusted risk ratio [aRR], 1.58) increased the risk of CHIKV infection, whereas ≥4 municipal trash collections/week (aRR, 0.38) and having externally piped water (aRR, 0.52) protected against CHIKV infection. Among 63 active and incident infections, 31 (49% [95% confidence interval {CI}, 36%, 62%]) were asymptomatic, yielding a ratio of symptomatic to asymptomatic infections of 1:0.97 (95% CI, 1:0.56, 1:1.60). Although our estimate is outside the 3% to 28% range reported previously, Bayesian and simulation analyses, informed by a systematic literature search, suggested that the proportion of inapparent CHIKV infections is lineage dependent and that more inapparent infections are associated with the Asian lineage than the East/Central/South African (ECSA) lineage. Overall, these data substantially improve knowledge regarding chikungunya epidemics.IMPORTANCE Chikungunya virus (CHIKV) is an understudied threat to human health. During the 2015 chikungunya epidemic in Managua, Nicaragua, we estimated the ratio of symptomatic to asymptomatic CHIKV infections, which is important for understanding transmission dynamics and the public health impact of CHIKV. This index cluster study identified and monitored persons at risk of infection, enabling capture of asymptomatic infections. We estimated that 31 (49%) of 63 at-risk participants had asymptomatic CHIKV infections, which is significantly outside the 3% to 28% range reported in literature reviews. However, recent seroprevalence studies, including two large pediatric cohort studies in the same setting, had also found percentages of inapparent infections outside the 3% to 28% range. Bayesian and simulation analyses, informed by a systematic literature search, revealed that the percentage of inapparent infections in epidemic settings varies by CHIKV phylogenetic lineage. Our study quantifies and provides the first epidemiological evidence that chikungunya epidemic characteristics are strongly influenced by CHIKV lineage.

Prior dengue virus infection and risk of Zika: A pediatric cohort in Nicaragua.

BACKGROUND: Zika virus (ZIKV) emerged in northeast Brazil in 2015 and spread rapidly across the Americas, in populations that have been largely exposed to dengue virus (DENV). The impact of prior DENV infection on ZIKV infection outcome remains unclear. To study this potential impact, we analyzed the large 2016 Zika epidemic in Managua, Nicaragua, in a pediatric cohort with well-characterized DENV infection histories. METHODS AND FINDINGS: Symptomatic ZIKV infections (Zika cases) were identified by real-time reverse transcription PCR and serology in a community-based cohort study that follows approximately 3,700 children aged 2-14 years old. Annual blood samples were used to identify clinically inapparent ZIKV infections using a novel, well-characterized serological assay. Multivariable Poisson regression was used to examine the relation between prior DENV infection and incidence of symptomatic and inapparent ZIKV infection. The generalized-growth method was used to estimate the effective reproduction number. From January 1, 2016, to February 28, 2017, 560 symptomatic ZIKV infections and 1,356 total ZIKV infections (symptomatic and inapparent) were identified, for an overall incidence of 14.0 symptomatic infections (95% CI: 12.9, 15.2) and 36.5 total infections (95% CI: 34.7, 38.6) per 100 person-years. Effective reproduction number estimates ranged from 3.3 to 3.4, depending on the ascending wave period. Incidence of symptomatic and total ZIKV infections was higher in females and older children. Analysis of the effect of prior DENV infection was performed on 3,027 participants with documented DENV infection histories, of which 743 (24.5%) had experienced at least 1 prior DENV infection during cohort follow-up. Prior DENV infection was inversely associated with risk of symptomatic ZIKV infection in the total cohort population (incidence rate ratio [IRR]: 0.63; 95% CI: 0.48, 0.81; p < 0.005) and with risk of symptomatic presentation given ZIKV infection (IRR: 0.62; 95% CI: 0.44, 0.86) when adjusted for age, sex, and recent DENV infection (1-2 years before ZIKV infection). Recent DENV infection was significantly associated with decreased risk of symptomatic ZIKV infection when adjusted for age and sex, but not when adjusted for prior DENV infection. Prior or recent DENV infection did not affect the rate of total ZIKV infections. Our findings are limited to a pediatric population and constrained by the epidemiology of the site. CONCLUSIONS: These findings support that prior DENV infection may protect individuals from symptomatic Zika. More research is needed to address the possible immunological mechanism(s) of cross-protection between ZIKV and DENV and whether DENV immunity also modulates other ZIKV infection outcomes such as neurological or congenital syndromes.

Neutralizing antibody titers against dengue virus correlate with protection from symptomatic infection in a longitudinal cohort.

The four dengue virus serotypes (DENV1-4) are mosquito-borne flaviviruses that infect ∼ 390 million people annually; up to 100 million infections are symptomatic, and 500,000 cases progress to severe disease. Exposure to a heterologous DENV serotype, the specific infecting DENV strains, and the interval of time between infections, as well as age, ethnicity, genetic polymorphisms, and comorbidities of the host, are all risk factors for severe dengue. In contrast, neutralizing antibodies (NAbs) are thought to provide long-lived protection against symptomatic infection and severe dengue. The objective of dengue vaccines is to provide balanced protection against all DENV serotypes simultaneously. However, the association between homotypic and heterotypic NAb titers and protection against symptomatic infection remains poorly understood. Here, we demonstrate that the titer of preinfection cross-reactive NAbs correlates with reduced likelihood of symptomatic secondary infection in a longitudinal pediatric dengue cohort in Nicaragua. The protective effect of NAb titers on infection outcome remained significant when controlled for age, number of years between infections, and epidemic force, as well as with relaxed or more stringent criteria for defining inapparent DENV infections. Further, individuals with higher NAb titers immediately after primary infection had delayed symptomatic infections compared with those with lower titers. However, overall NAb titers increased modestly in magnitude and remained serotype cross-reactive in the years between infections, possibly due to reexposure. These findings establish that anti-DENV NAb titers correlate with reduced probability of symptomatic DENV infection and provide insights into longitudinal characteristics of antibody-mediated immunity to DENV in an endemic setting.

Obesity Increases the Duration of Influenza A Virus Shedding in Adults.

Epidemiologic studies indicate that obesity increases the risk of severe complications and death from influenza virus infections, especially in elderly individuals. This work investigates the effect of obesity on the duration of viral shedding within household transmission studies in Managua, Nicaragua, over 3 seasons (2015-2017). Symptomatic obese adults were shown to shed influenza A virus 42% longer than nonobese adults (adjusted event time ratio [ETR], 1.42; 95% confidence interval [CI], 1.06-1.89); no association was observed with influenza B virus shedding duration. Even among paucisymptomatic and asymptomatic adults, obesity increased the influenza A shedding duration by 104% (adjusted ETR, 2.04; 95% CI, 1.35-3.09). These findings suggest that obesity may play an important role in influenza transmission.

Differences in Transmission and Disease Severity Between 2 Successive Waves of Chikungunya.

Background: Chikungunya, an arboviral disease, caused massive epidemics in Central and South America in 2014-2016. In a prospective pediatric cohort study, we examined the introduction of chikungunya in a naive population and investigated transmission and clinical characteristics. Methods: Children presenting to the study health center with a chikungunya-like illness or undifferentiated fever were tested for chikungunya virus (CHIKV) infection by reverse transcriptase-polymerase chain reaction (RT-PCR) and serological assays. Inapparent CHIKV infections in the intervening year were determined by seroconversion in healthy blood samples collected annually. Results: A total of 4353 children participated in the cohort study from March 2014 to February 2016 during the 2 epidemic waves of chikungunya. A total of 539 cases of chikungunya were documented, for an incidence rate of 80.2 cases per 1000 person-years (95% confidence interval [CI]: 73.7, 87.2); and a total of 893 CHIKV infections were documented, for an incidence rate of 137.1 infections per 1000 person-years (95% CI: 128.4, 146.4). The seroprevalence of anti-CHIKV antibodies increased linearly with age, with seroprevalence of >45% in 14-year-old children at the end of Epidemic 2. Symptom presentation varied between the epidemics, with Epidemic 2 exhibiting both a higher symptomatic-to-inapparent ratio (1:1.20 in Epidemic 1 vs. 1:0.65 in Epidemic 2) and more severe clinical presentation among cases. The mean reproduction number was also greater in Epidemic 2 than in Epidemic 1. Conclusions: The intensity of transmission and severity of clinical presentation varied between the 2 epidemics, with higher transmission intensity associated with greater disease severity.

Influenza Transmission Dynamics in Urban Households, Managua, Nicaragua, 2012-2014.

During August 2012-November 2014, we conducted a case ascertainment study to investigate household transmission of influenza virus in Managua, Nicaragua. We collected up to 5 respiratory swab samples from each of 536 household contacts of 133 influenza virus-infected persons and assessed for evidence of influenza virus transmission. The overall risk for influenza virus infection of household contacts was 15.7% (95% CI 12.7%-19.0%). Oseltamivir treatment of index patients did not appear to reduce household transmission. The mean serial interval for within-household transmission was 3.1 (95% CI 1.6-8.4) days. We found the transmissibility of influenza B virus to be higher than that of influenza A virus among children. Compared with households with <4 household contacts, those with >4 household contacts appeared to have a reduced risk for infection. Further research is needed to model household influenza virus transmission and design interventions for these settings.

Characterization of Dengue Virus Infections Among Febrile Children Clinically Diagnosed With a Non-Dengue Illness, Managua, Nicaragua.

Background: We sought to characterize dengue virus (DENV) infections among febrile children enrolled in a pediatric cohort study who were clinically diagnosed with a non-dengue illness ("C cases"). Methods: DENV infections were detected and viral load quantitated by real-time reverse transcription-polymerase chain reaction in C cases presenting between January 2007 and January 2013. Results: One hundred forty-one of 2892 C cases (4.88%) tested positive for DENV. Of all febrile cases in the study, DENV-positive C cases accounted for an estimated 52.0% of patients with DENV viremia at presentation. Compared with previously detected, symptomatic dengue cases, DENV-positive C cases were significantly less likely to develop long-lasting humoral immune responses to DENV, as measured in healthy annual serum samples (79.7% vs 47.8%; P < .001). Humoral immunity was associated with viral load at presentation: 40 of 43 patients (93.0%) with a viral load ≥7.0 log10 copies/mL serum developed the expected rise in anti-DENV antibodies in annual samples versus 13 of 68 (19.1%) patients with a viral load below this level (P < .001). Conclusions: Antibody responses to DENV-positive C cases differ from responses to classic symptomatic dengue. These findings have important implications for DENV transmission modeling, immunology, and epidemiologic surveillance.