Quantifying the relationship between arboviral infection prevalence and human mobility patterns among participants of the Communities Organized to Prevent Arboviruses cohort (COPA) in southern Puerto Rico.

Human movement is increasingly being recognized as a major driver of arbovirus risk and dissemination. The Communities Organized to Prevent Arboviruses (COPA) study is a cohort in southern Puerto Rico to measure arboviral prevalence, evaluate interventions, and collect mobility data. To quantify the relationship between arboviral prevalence and human mobility patterns, we fit multilevel logistic regression models to estimate odds ratios for mobility-related predictors of positive chikungunya IgG or Zika IgM test results collected from COPA, assuming mobility data does not change substantially from year to year. From May 8, 2018-June 8, 2019, 39% of the 1,845 active participants during the study period had a positive arboviral seroprevalence result. Most (74%) participants reported spending five or more weekly hours outside of their home. A 1% increase in weekly hours spent outside the home was associated with a 4% (95% confidence interval (CI): 2-7%) decrease in the odds of testing positive for arbovirus. After adjusting for age and whether a person had air conditioning (AC) at home, any time spent in a work location was protective against arbovirus infection (32% decrease, CI: 9-49%). In fact, there was a general decreased prevalence for individuals who visited locations that were inside and had AC or screens, regardless of the type of location (32% decrease, CI: 12-47%). In this population, the protective characteristics of locations visited appear to be the most important driver of the relationship between mobility and arboviral prevalence. This relationship indicates that not all mobility is the same, with elements like screens and AC providing protection in some locations. These findings highlight the general importance of AC and screens, which are known to be protective against mosquitoes and mosquito-transmitted diseases.

Cost-effectiveness analysis of typhoid conjugate vaccines in an outbreak setting: a modeling study.

BACKGROUND: Several prolonged typhoid fever epidemics have been reported since 2010 throughout eastern and southern Africa, including Malawi, caused by multidrug-resistant Salmonella Typhi. The World Health Organization recommends the use of typhoid conjugate vaccines (TCVs) in outbreak settings; however, current data are limited on how and when TCVs might be introduced in response to outbreaks. METHODOLOGY: We developed a stochastic model of typhoid transmission fitted to data from Queen Elizabeth Central Hospital in Blantyre, Malawi from January 1996 to February 2015. We used the model to evaluate the cost-effectiveness of vaccination strategies over a 10-year time horizon in three scenarios: (1) when an outbreak is likely to occur; (2) when an outbreak is unlikely to occur within the next ten years; and (3) when an outbreak has already occurred and is unlikely to occur again. We considered three vaccination strategies compared to the status quo of no vaccination: (a) preventative routine vaccination at 9 months of age; (b) preventative routine vaccination plus a catch-up campaign to 15 years of age; and (c) reactive vaccination with a catch-up campaign to age 15 (for Scenario 1). We also explored variations in outbreak definitions, delays in implementation of reactive vaccination, and the timing of preventive vaccination relative to the outbreak. RESULTS: Assuming an outbreak occurs within 10 years, we estimated that the various vaccination strategies would prevent a median of 15-60% of disability-adjusted life-years (DALYs). Reactive vaccination was the preferred strategy for WTP values of $0-300 per DALY averted. For WTP values > $300, introduction of preventative routine TCV immunization with a catch-up campaign was the preferred strategy. Routine vaccination with a catch-up campaign was cost-effective for WTP values above $890 per DALY averted if no outbreak occurs and > $140 per DALY averted if implemented after the outbreak has already occurred. CONCLUSIONS: Countries for which the spread of antimicrobial resistance is likely to lead to outbreaks of typhoid fever should consider TCV introduction. Reactive vaccination can be a cost-effective strategy, but only if delays in vaccine deployment are minimal; otherwise, introduction of preventive routine immunization with a catch-up campaign is the preferred strategy.

Burden of enteric fever at three urban sites in Africa and Asia: a multicentre population-based study.

BACKGROUND: Enteric fever is a serious public health concern in many low-income and middle-income countries. Numerous data gaps exist concerning the epidemiology of Salmonella enterica serotype Typhi (S Typhi) and Salmonella enterica serotype Paratyphi (S Paratyphi), which are the causative agents of enteric fever. We aimed to determine the burden of enteric fever in three urban sites in Africa and Asia. METHODS: In this multicentre population-based study, we did a demographic census at three urban sites in Africa (Blantyre, Malawi) and Asia (Kathmandu, Nepal and Dhaka, Bangladesh) between June 1, 2016, and Sept 25, 2018. Households were selected randomly from the demographic census. Participants from within the geographical census area presenting to study health-care facilities were approached for recruitment if they had a history of fever for 72 h or more (later changed to >48 h) or temperature of 38·0°C or higher. Facility-based passive surveillance was done between Nov 11, 2016, and Dec 31, 2018, with blood-culture collection for febrile illness. We also did a community-based serological survey to obtain data on Vi-antibody defined infections. We calculated crude incidence for blood-culture-confirmed S Typhi and S Paratyphi infection, and calculated adjusted incidence and seroincidence of S Typhi blood-culture-confirmed infection. FINDINGS: 423 618 individuals were included in the demographic census, contributing 626 219 person-years of observation for febrile illness surveillance. 624 S Typhi and 108 S Paratyphi A isolates were collected from the blood of 12 082 febrile patients. Multidrug resistance was observed in 44% S Typhi isolates and fluoroquinolone resistance in 61% of S Typhi isolates. In Blantyre, the overall crude incidence of blood-culture confirmed S Typhi was 58 cases per 100 000 person-years of observation (95% CI 48-70); the adjusted incidence was 444 cases per 100 000 person-years of observation (95% credible interval [CrI] 347-717). The corresponding rates were 74 (95% CI 62-87) and 1062 (95% CrI 683-1839) in Kathmandu, and 161 (95% CI 145-179) and 1135 (95% CrI 898-1480) in Dhaka. S Paratyphi was not found in Blantyre; overall crude incidence of blood-culture-confirmed S Paratyphi A infection was 6 cases per 100 000 person-years of observation (95% CI 3-11) in Kathmandu and 42 (95% CI 34-52) in Dhaka. Seroconversion rates for S Typhi infection per 100 000 person-years estimated from anti-Vi seroconversion episodes in serological surveillance were 2505 episodes (95% CI 1605-3727) in Blantyre, 7631 (95% CI 5913-9691) in Kathmandu, and 3256 (95% CI 2432-4270) in Dhaka. INTERPRETATION: High disease incidence and rates of antimicrobial resistance were observed across three different transmission settings and thus necessitate multiple intervention strategies to achieve global control of these pathogens. FUNDING: Wellcome Trust and the Bill & Melinda Gates Foundation.

A Bayesian approach for estimating typhoid fever incidence from large-scale facility-based passive surveillance data.

Decisions about typhoid fever prevention and control are based on estimates of typhoid incidence and their uncertainty. Lack of specific clinical diagnostic criteria, poorly sensitive diagnostic tests, and scarcity of accurate and complete datasets contribute to difficulties in calculating age-specific population-level typhoid incidence. Using data from the Strategic Typhoid Alliance across Africa and Asia program, we integrated demographic censuses, healthcare utilization surveys, facility-based surveillance, and serological surveillance from Malawi, Nepal, and Bangladesh to account for under-detection of cases. We developed a Bayesian approach that adjusts the count of reported blood-culture-positive cases for blood culture detection, blood culture collection, and healthcare seeking-and how these factors vary by age-while combining information from prior published studies. We validated the model using simulated data. The ratio of observed to adjusted incidence rates was 7.7 (95% credible interval [CrI]: 6.0-12.4) in Malawi, 14.4 (95% CrI: 9.3-24.9) in Nepal, and 7.0 (95% CrI: 5.6-9.2) in Bangladesh. The probability of blood culture collection led to the largest adjustment in Malawi, while the probability of seeking healthcare contributed the most in Nepal and Bangladesh; adjustment factors varied by age. Adjusted incidence rates were within or below the seroincidence rate limits of typhoid infection. Estimates of blood-culture-confirmed typhoid fever without these adjustments results in considerable underestimation of the true incidence of typhoid fever. Our approach allows each phase of the reporting process to be synthesized to estimate the adjusted incidence of typhoid fever while correctly characterizing uncertainty, which can inform decision-making for typhoid prevention and control.

Correction: Changes in historical typhoid transmission across 16 U.S. cities, 1889-1931: Quantifying the impact of investments in water and sewer infrastructures.

[This corrects the article DOI: 10.1371/journal.pntd.0008048.].

Evaluating post-vaccine expansion patterns of pneumococcal serotypes.

BACKGROUND: Streptococcus pneumoniae remains a leading cause of morbidity and mortality. Pneumococcal conjugate vaccines (PCVs) are effective but target only a fraction of the more than 90 pneumococcal serotypes. As a result, the introduction of PCVs has been followed by the emergence of non-vaccine serotypes. With higher-valency PCVs currently under development, there is a need to understand and predict patterns of serotype replacement to anticipate future changes. METHODS: In this study, we fit a hierarchical Bayesian regression model to evaluate patterns of change in serotype prevalence post-PCV introduction in Israel from 2009 to 2016. RESULTS: We found that the assumption that non-vaccine serotypes increase by the same proportion overestimates changes in serotype prevalence in Jewish and Bedouin children. Furthermore, pre-vaccine prevalence was positively associated with increases in prevalence over the study period. From our analyses, serotypes 12F, 8, 16F, 33F, 9N, 7B, 10A, 22F, 24F, and 17F were estimated to have gained the most cases of invasive pneumococcal disease through serotype replacement in the Jewish population. However, this model also failed to quantify some additional cases gained, suggesting that changes in carriage in children alone may be insufficient to explain serotype replacement in disease. CONCLUSIONS: Understanding of serotype replacement is important as higher-valency vaccines are introduced.

Changes in historical typhoid transmission across 16 U.S. cities, 1889-1931: Quantifying the impact of investments in water and sewer infrastructures.

Investments in water and sanitation systems are believed to have led to the decline in typhoid fever in developed countries, such that most cases now occur in regions lacking adequate clean water and sanitation. Exploring seasonal and long-term patterns in historical typhoid mortality in the United States can offer deeper understanding of disease drivers. We fit modified Time-series Susceptible-Infectious-Recovered models to city-level weekly mortality counts to estimate seasonal and long-term typhoid transmission. We examined seasonal transmission separately by city and aggregated by water source. Typhoid transmission peaked in late summer/early fall. Seasonality varied by water source, with the greatest variation occurring in cities with reservoirs. We then fit hierarchical regression models to measure associations between long-term transmission and annual financial investments in water and sewer systems. Overall historical $1 per capita ($16.13 in 2017) investments in the water supply were associated with approximately 5% (95% confidence interval: 3-6%) decreases in typhoid transmission, while $1 increases in the overall sewer system investments were associated with estimated 6% (95% confidence interval: 4-9%) decreases. Our findings aid in the understanding of typhoid transmission dynamics and potential impacts of water and sanitation improvements, and can inform cost-effectiveness analyses of interventions to reduce the typhoid burden.

Water and Filth: Reevaluating the First Era of Sanitary Typhoid Intervention (1840-1940).

While typhoid fever remains an important cause of illness in many low- and middle-income countries, important insights can be learned by exploring the historical experience with typhoid fever in industrialized countries. We used archival research to examine British and American attempts to control typhoid via sanitary interventions from the 1840s to 1940s. First, we assess how varying perceptions of typhoid and conflicts of interest led to a nonlinear evolution of control attempts in Oxford, United Kingdom. Our qualitative analysis shows how professional rivalries and tensions between Oxford's university and citizens ("gown and town"), as well as competing theories of typhoid proliferation stalled sanitary reform until the provision of cheap external credit created cross-party alliances at the municipal level. Second, we use historical mortality data to evaluate and quantify the impact of individual sanitary measures on typhoid transmission in major US cities. Together a historiographic and epidemiological study of past interventions provides insights for the planning of future sanitary programs.

Risk factors associated with life jacket wear among adult canoeists and kayakers in the United States, 1999-2017.

Drowning is the most common cause of death in recreational boating. Life jackets prevent drowning, yet adult wear rates remain relatively low on most types of boats. Canoes and kayaks are among the least used boat types, yet maintain the third and first highest annual boating-related drowning rates in 2012, respectively. This 1999-2017 study collected data from 124 study sites across the US. Life jacket wear was calculated for 13 dichotomized risky and non-risky variables, using Chi-square tests. A count variable based on number of risks was created, and Cochran-Armitage trend tests examined linearity in life jacket use. Three illustrative variables for each boat type were represented in tree diagrams. Kayakers had higher wear rates than canoeists among all variables observed. For both boats, the majority of risky conditions had higher life jacket wear rates than their non-risky alternatives. As the number of risks increased, life jacket wear rate increased. Boaters seemingly conduct a mental assessment of risk to determine whether to wear a life jacket.

Factors associated with life jacket use among cabin sailboat and day sailor boaters in the United States.

INTRODUCTION: In 2015, drowning accounted for 68% of the 626 recreational boating related deaths in the United States. Although life jackets are estimated to prevent between 50% to 80% of boating deaths, approximately 83% of sailboat-related drowning victims were reported to not be wearing life jackets. Life jacket use among adult boaters has remained consistently low across most boat types and may vary by boater, boating, and environmental conditions. Although many risky environmental and boating factors may be associated with a higher risk of boating death, drowning occurs in all situations and it is useful to understand adult life jacket wearing behaviors in differing boating situations. METHODS: This study uses observational survey data from 61318 adult sailors collected during the summer months of 1999 - 2017 from 124 selected study sites across 30 states in the US. Life jacket use was compared for day sailors and cabin sailboats by multiple boating, boater, and environmental conditions using Chi-square tests for equality of proportions. Results of these tests led to a choice of 3 informative and scientifically compelling variables to summarize variation in life jacket use for each sailboat type. Odds ratios were calculated comparing life jacket use from each boating situation to the lowest risk situation as determined by the 3 selected variables. These variables were represented in a tree diagram, detailing the additive impact of each factor. Following these analyses, all boating conditions were categorized to be risky or non-risky and a count variable was created for each observation based on the number of risks present. Cochran-Armitage trend tests were conducted to test for linearity in life jacket use for both boat types. RESULTS: The overall life jacket wear rate was higher among adults in day sailor sailboats (51.6%) compared to cabin sailboats (13.8%) and in all measured demographic, boating, and environmental circumstances. Comparing high-risk cabin sailboat conditions of low water temperatures, small boat size, and high wind speed to the lowest-risk situation accounted for a 23.3% range in life jacket wear rate (OR=4.7). Comparing high-risk day sailor sailboat conditions of small boat size, one boater on board, and choppy/rough wave height to the lowest-risk situation accounted for a 39.3% range in life jacket wear rate (OR=5.9). For both boat types, the number of risks present and life jacket wear rate exhibited a statistically significant positive linear relationship at p<0.0001. CONCLUSION: Study results suggest that boaters are aware of the connection between life jacket use and drowning prevention and are more likely to wear life jackets when boating in conditions perceived to be risky. PRACTICAL APPLICATIONS: Boating safety promotion efforts should recommend adult life jacket use in all boating situations, as seemingly non-risky conditions may still result in drownings.