Frequency of respiratory virus-associated infection among children and adolescents from a tertiary-care hospital in Mexico City.

Acute respiratory infections (ARIs) are a major cause of morbidity and mortality among children. The causative pathogens show geographic and seasonal variations. We retrospectively evaluated the frequency and seasonality of respiratory pathogens in children and adolescents (age: 0-19 years) with ARIs treated between January 1, 2021, and March 31, 2022, at a single center in Mexico. Out of 2400 patients, 1,603 were diagnosed with SARS-CoV-2 infection and 797 were diagnosed with other common respiratory pathogens (CRPs). Of the 797 patients, 632 were infected with one CRP and 165 with > 2 CRPs. Deaths occurred only in SARS-CoV-2-infected patients. Rhinovirus/Enterovirus, respiratory syncytial virus B, and parainfluenza virus 3 were the most prevalent in cases with single and multiple infections. CRP showed a high frequency between autumn and winter of 2021, with higher incidence of hospitalization compared to COVID-19. The main comorbidities were immunosuppression, cardiovascular disease (CD), and asthma. The frequency of CRPs showed a downward trend throughout the first half of 2021. CRPs increased in single- and co-infection cases between the fourth and fifth waves of COVID-19, probably due to decreased nonpharmaceutical interventions and changes in diagnostic tests. Age, cyanosis (symptom), and immunosuppression (comorbidity) were found to differentiate between SARS-CoV-2 infection and CRP infection.

Metagenomic analysis reveals differences in the co-occurrence and abundance of viral species in SARS-CoV-2 patients with different severity of disease.

BACKGROUND: SARS-CoV-2 infections have a wide spectrum of clinical manifestations whose causes are not completely understood. Some human conditions predispose to severe outcome, like old age or the presence of comorbidities, but many other facets, including coinfections with other viruses, remain poorly characterized. METHODS: In this study, the eukaryotic fraction of the respiratory virome of 120 COVID-19 patients was characterized through whole metagenomic sequencing. RESULTS: Genetic material from respiratory viruses was detected in 25% of all samples, whereas human viruses other than SARS-CoV-2 were found in 80% of them. Samples from hospitalized and deceased patients presented a higher prevalence of different viruses when compared to ambulatory individuals. Small circular DNA viruses from the Anneloviridae (Torque teno midi virus 8, TTV-like mini virus 19 and 26) and Cycloviridae families (Human associated cyclovirus 10), Human betaherpesvirus 6, were found to be significantly more abundant in samples from deceased and hospitalized patients compared to samples from ambulatory individuals. Similarly, Rotavirus A, Measles morbillivirus and Alphapapilomavirus 10 were significantly more prevalent in deceased patients compared to hospitalized and ambulatory individuals. CONCLUSIONS: Results show the suitability of using metagenomics to characterize a broader peripheric virological landscape of the eukaryotic virome in SARS-CoV-2 infected patients with distinct disease outcomes. Identified prevalent viruses in hospitalized and deceased patients may prove important for the targeted exploration of coinfections that may impact prognosis.

Genomic Characterization of SARS-CoV-2 Isolated from Patients with Distinct Disease Outcomes in Mexico.

The coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has shown a wide spectrum of clinical manifestations ranging from asymptomatic infections to severe disease and death. Pre-existing medical conditions and age have been mainly linked to the development of severe disease; however, the potential association of viral genetic characteristics with different clinical conditions remains unclear. SARS-CoV-2 variants with increased transmissibility were detected early in the pandemics, and several variants with potential relevance for public health are currently circulating around the world. In this study, we characterized 57 complete SARS-CoV-2 genomes during the exponential growth phase of the early epidemiological curve in Mexico, in April 2020. Patients were categorized under distinct disease severity outcomes: mild disease or ambulatory care, severe disease or hospitalized, and deceased. To reduce bias related to risk factors, the patients were less than 60 years old and with no diagnosed comorbidities A trait-association phylogenomic approach was used to explore genotype-phenotype associations, represented by the co-occurrence of mutations, disease severity outcome categories, and clusters of Mexican sequences. Phylogenetic results revealed a higher genomic diversity compared to the initial viruses detected during the early stage of the local epidemic. We identified a total of 90 single nucleotide variants compared to the Wuhan-Hu-1 genome, including 54 nonsynonymous mutations. We did not find evidence for the co-occurrence of mutations associated with specific disease outcomes. Therefore, in the group of patients studied, disease severity was likely mainly driven by the host genetic background and other demographic factors. IMPORTANCE The genetic association of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) with different clinical conditions remains unclear and needs further investigation. In this study, we characterized 57 complete SARS-CoV-2 genomes from patients in Mexico with distinct disease severity outcomes: mild disease or ambulatory care, severe disease or hospitalized, and deceased. To reduce bias related to risk factors the patients were less than 60 years old and with no diagnosed comorbidities. We did not find evidence for the co-occurrence of mutations associated with specific disease outcomes. Therefore, in the group of patients studied, disease severity was likely mainly driven by the host genetic background and other demographic factors.

Genetic Analysis of SARS-CoV-2 Variants in Mexico during the First Year of the COVID-19 Pandemic.

During the first year of the SARS-CoV-2 pandemic in Mexico, more than two million people were infected. In this study, we analyzed full genome sequences from 27 February 2020 to 28 February 2021 to characterize the geographical and temporal distribution of SARS-CoV-2 lineages and identify the most common circulating lineages during this period. We defined six different geographical regions with particular dynamics of lineage circulation. The Northeast and Northwest regions were the ones that exhibited the highest lineage diversity, while the Central south and South/Southeast regions presented less diversity with predominance of a certain lineage. Additionally, by late February 2021, lineage B.1.1.519 represented more than 89% of all circulating lineages in the country.

Emergence and spread of the potential variant of interest (VOI) B.1.1.519 of SARS-CoV-2 predominantly present in Mexico.

SARS-CoV-2 variants emerged in late 2020, and at least three variants of concern (B.1.1.7, B.1.351, and P1) have been reported by WHO. These variants have several substitutions in the spike protein that affect receptor binding; they exhibit increased transmissibility and may be associated with reduced vaccine effectiveness. In the present work, we report the identification of a potential variant of interest, harboring the mutations T478K, P681H, and T732A in the spike protein, within the newly named lineage B.1.1.519, that rapidly outcompeted the preexisting variants in Mexico and has been the dominant virus in the country during the first trimester of 2021.

Genomic Analysis of Early SARS-CoV-2 Variants Introduced in Mexico.

The coronavirus disease 2019 (COVID-19) pandemic has affected most countries in the world. Studying the evolution and transmission patterns in different countries is crucial to enabling implementation of effective strategies for disease control and prevention. In this work, we present the full genome sequence for 17 SARS-CoV-2 isolates corresponding to the earliest sampled cases in Mexico. Global and local phylogenomics, coupled with mutational analysis, consistently revealed that these viral sequences are distributed within 2 known lineages, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) lineage A/G, containing mostly sequences from North America, and lineage B/S, containing mainly sequences from Europe. Based on the exposure history of the cases and on the phylogenomic analysis, we characterized 14 independent introduction events. Additionally, three cases with no travel history were identified. We found evidence that two of these cases represented local transmission cases occurring in Mexico during mid-March 2020, denoting the earliest events described for the country. Within this local transmission cluster, we also identified an H49Y amino acid change in the Spike protein. This mutation represents a homoplasy occurring independently through time and space and may function as a molecular marker to follow any further spread of these viral variants throughout the country. Our results provide a general picture of the SARS-CoV-2 variants introduced at the beginning of the outbreak in Mexico, setting the foundation for future surveillance efforts.IMPORTANCE Understanding the introduction, spread, and establishment of SARS-CoV-2 within distinct human populations as well as the evolution of the pandemics is crucial to implement effective control strategies. In this work, we report that the initial virus strains introduced in Mexico came from Europe and the United States and that the virus was circulating locally in the country as early as mid-March. We also found evidence for early local transmission of strains with a H49Y mutation in the Spike protein, which could be further used as a molecular marker to follow viral spread within the country and the region.

Full genome sequence of the first SARS-CoV-2 detected in Mexico.

SARS-CoV-2 was first detected in the city of Wuhan, Hubei Province, China. In this report, we describe the complete genome sequence of the first imported SARS-CoV-2, detected in a Mexican patient who had traveled to Bergamo, Italy. Phylogenetic analysis showed that this isolate belongs to subclade A2a (lineage G) and is closely related to isolates from Finland, Germany and Brazil, all of which were from patients with a history of travel to Italy. This is the first report of the complete genome sequence of this virus in Mexico.

Human Metapneumovirus: Etiological Agent of Severe Acute Respiratory Infections in Hospitalized and Deceased Patients with a Negative Diagnosis of Influenza.

Human metapneumovirus (HMPV) is one of the four major viral pathogens associated with acute respiratory tract infections (ARI) and creates a substantial burden of disease, particularly in young children (<5 years) and older individuals (≥65 years). The objective of this study was to determine the epidemiological behavior of HMPV in Mexico. This retrospective study was conducted over a nine-year period and used 7283 influenza-negative respiratory samples from hospitalized and deceased patients who presented Severe Acute Respiratory Infection (SARI). The samples were processed with the help of qualitative multiplex RT-PCR for simultaneous detection of 14 respiratory viruses (xTAG® RVP FAST v2). 40.8% of the samples were positive for respiratory viruses, mainly rhinovirus/enterovirus (47.6%), respiratory syncytial virus (15.9%), HMPV (11.1%) and parainfluenza virus (8.9%). Other respiratory viruses and co-infections accounted for 16.5%. HMPV infects all age groups, but the most affected group was infants between 29 days and 9 years of age (65.6%) and adults who are 40 years and older (25.7%). HMPV circulates every year from November to April, and the highest circulation was observed in late winter. The results of this study aim to raise awareness among clinicians about the high epidemiological impact of HMPV in young children and older individuals in order to reduce the economic burden in terms of health care costs.

Complete genome sequence of a coxsackievirus type A24 variant causing an outbreak of acute haemorrhagic conjunctivitis in southeastern Mexico in 2017.

Cases of acute haemorrhagic conjunctivitis (AHC) caused by a coxsackie virus A24 variant (CV-A24v) in Mexico have been reported since 1987; however, no molecular data on the causative strains have been available. Here, we report the identification of the etiological agent responsible for the most recent AHC outbreak in southeastern Mexico (at the end of 2017) as well as the complete genome sequences of seven isolates, using next-generation sequencing (NGS). Phylogenomic analysis of the CV-A24v sequences reported here showed similarity to contemporary strains causing AHC outbreaks in French Guiana and Uganda, forming a novel clade related to genotype IV. Moreover, a specific mutational pattern in the non-structural proteins was identified in the 2017 isolates. This is the first report of genetic characterization of CV-A24v isolates obtained in Mexico.

Surveillance for the identification of cases of acute respiratory infection by enterovirus D68 in children in a tertiary level care hospital during 2014-2016. / Vigilancia epidemiológica para la identificación de casos de infección respiratoria aguda por enterovirus D68 en niños en un hospital de tercer nivel de atención durante 2014-2016

Background: The reemergence of enterovirus D68 (EV-D68) infections in the United States was reported from August-October 2014 (691 cases). In Mexico, an outbreak at the National Institute of Respiratory Diseases was reported (24 cases). The results of epidemiological surveillance of Enterovirus sp. (EV) and other respiratory viruses in a national pediatric tertiary care level hospital are presented. Methods: Following the alert issued by the reemergence of EV-D68 in 2014, epidemiological surveillance -which only detected respiratory viruses by PCR in patients with influenza-like illness using nasopharyngeal swabs- expanded to include children with asthma exacerbation or acute respiratory distress. Positive samples to EV were confirmed and typed by sequencing. Subsequent sequencing was used to obtain the complete viral genome. Results: Of 1705 samples, 13 were positive to EV. Patients with EV presented the following comorbidities: chronic lung disease (7.7%), neoplastic disease (15.4%), allergic asthma/rhinitis (23%), recurrent pneumonia (23%), and other (23%). Of the 13 samples positive for EV, three were positive for EV-D68. These cases required invasive mechanical ventilation, presented no neurological involvement and survived. Conclusions: The impact of the population studied by EV-D68 was lower than that reported in Mexico during the same period. Cases of EV-D68 infection had multiple comorbidities, but few pulmonary comorbidities, which could explain the low attack rate. The epidemiological surveillance and infection prevention system may have contained the outbreak.

Introducción: La reemergencia de las infecciones por Enterovirus D68 (EV-D68) se reportó en los EE.UU. desde agosto-octubre de 2014 (691 casos). En México, un brote se reportó en el Instituto Nacional de Enfermedades Respiratorias (24 casos). Se presentan los resultados de la vigilancia epidemiológica en un hospital pediátrico nacional de tercer nivel para Enterovirus sp. (EV) y otros virus respiratorios. Método: Tras la alerta emitida por la reemergencia del EV-D68 en 2014, la vigilancia epidemiológica ­que solo detectaba virus respiratorios mediante PCR en pacientes con enfermedad tipo influenza mediante toma de hisopados nasofaríngeos­ se expandió para incluir niños con exacerbación de asma o dificultad respiratoria aguda. Las muestras positivas para EV fueron confirmadas y tipificadas por secuenciación. Posteriormente, se utilizó secuenciación de siguiente generación para obtener el genoma viral completo. Resultados: De 1705 muestras, 13 fueron positivas para EV. Los pacientes con EV presentaron la siguiente comorbilidad: enfermedad pulmonar crónica (7.7%), enfermedad neoplásica (15.4%), asma/rinitis alérgica (23%), neumonías de repetición (23%), y otras (23%). De las 13 muestras positivas para EV, tres resultaron positivas para EV-D68. Dichos casos requirieron ventilación mecánica invasiva, no tuvieron afectación neurológica y sobrevivieron. Conclusiones: La afectación por EV-D68 de la población estudiada fue menor que lo reportado en México durante el mismo periodo. Los casos de infección por EV-D68 presentan diversa comorbilidad, aunque escasas enfermedades pulmonares, lo cual pudiera explicar la baja tasa de ataque. La presencia del sistema de vigilancia epidemiológica establecido y la prevención de infecciones pudieron haber contenido el brote.

Vigilancia epidemiológica para la identificación de casos de infección respiratoria aguda por enterovirus D68 en niños en un hospital de tercer nivel de atención durante 2014-2016 / Surveillance for the identification of cases of acute respiratory infection by enterovirus D68 in children in a tertiary level care hospital during 2014-2016

Resumen Introducción: La reemergencia de las infecciones por Enterovirus D68 (EV-D68) se reportó en los EE.UU. desde agosto-octubre de 2014 (691 casos). En México, un brote se reportó en el Instituto Nacional de Enfermedades Respiratorias (24 casos). Se presentan los resultados de la vigilancia epidemiológica en un hospital pediátrico nacional de tercer nivel para Enterovirus sp. (EV) y otros virus respiratorios. Método: Tras la alerta emitida por la reemergencia del EV-D68 en 2014, la vigilancia epidemiológica -que solo detectaba virus respiratorios mediante PCR en pacientes con enfermedad tipo influenza mediante toma de hisopados nasofaríngeos- se expandió para incluir niños con exacerbación de asma o dificultad respiratoria aguda. Las muestras positivas para EV fueron confirmadas y tipificadas por secuenciación. Posteriormente, se utilizó secuenciación de siguiente generación para obtener el genoma viral completo. Resultados: De 1705 muestras, 13 fueron positivas para EV. Los pacientes con EV presentaron la siguiente comorbilidad: enfermedad pulmonar crónica (7.7%), enfermedad neoplásica (15.4%), asma/rinitis alérgica (23%), neumonías de repetición (23%), y otras (23%). De las 13 muestras positivas para EV, tres resultaron positivas para EV-D68. Dichos casos requirieron ventilación mecánica invasiva, no tuvieron afectación neurológica y sobrevivieron. Conclusiones: La afectación por EV-D68 de la población estudiada fue menor que lo reportado en México durante el mismo periodo. Los casos de infección por EV-D68 presentan diversa comorbilidad, aunque escasas enfermedades pulmonares, lo cual pudiera explicar la baja tasa de ataque. La presencia del sistema de vigilancia epidemiológica establecido y la prevención de infecciones pudieron haber contenido el brote.

Abstract Background: The reemergence of enterovirus D68 (EV-D68) infections in the United States was reported from August-October 2014 (691 cases). In Mexico, an outbreak at the National Institute of Respiratory Diseases was reported (24 cases). The results of epidemiological surveillance of Enterovirus sp. (EV) and other respiratory viruses in a national pediatric tertiary care level hospital are presented. Methods: Following the alert issued by the reemergence of EV-D68 in 2014, epidemiological surveillance -which only detected respiratory viruses by PCR in patients with influenza-like illness using nasopharyngeal swabs- expanded to include children with asthma exacerbation or acute respiratory distress. Positive samples to EV were confirmed and typed by sequencing. Subsequent sequencing was used to obtain the complete viral genome. Results: Of 1705 samples, 13 were positive to EV. Patients with EV presented the following comorbidities: chronic lung disease (7.7%), neoplastic disease (15.4%), allergic asthma/rhinitis (23%), recurrent pneumonia (23%), and other (23%). Of the 13 samples positive for EV, three were positive for EV-D68. These cases required invasive mechanical ventilation, presented no neurological involvement and survived. Conclusions: The impact of the population studied by EV-D68 was lower than that reported in Mexico during the same period. Cases of EV-D68 infection had multiple comorbidities, but few pulmonary comorbidities, which could explain the low attack rate. The epidemiological surveillance and infection prevention system may have contained the outbreak.

Influenza seasonality goes south in the Yucatan Peninsula: The case for a different influenza vaccine calendar in this Mexican region.

INTRODUCTION: While vaccination may be relatively straightforward for regions with a well-defined winter season, the situation is quite different for tropical regions. Influenza activity in tropical regions might be out of phase with the dynamics predicted for their hemispheric group thereby impacting the effectiveness of the immunization campaign. OBJECTIVE: To investigate how the climatic diversity of Mexico hinders its existing influenza immunization strategy and to suggest that the hemispheric vaccine recommendations be tailored to the regional level in order to optimize vaccine effectiveness. METHODS: We studied the seasonality of influenza throughoutMexico by modeling virological and mortality data.De-trended time series of each Mexican state were analyzed by Fourier decomposition to describe the amplitude and timing of annual influenza epidemic cycles and to compare with each the timing of the WHO's Northern and Southern Hemispheric vaccination schedule. FINDINGS: The timings of the primary (major) peaks of both virological and mortality data for most Mexican states are well aligned with the Northern Hemisphere winter (December-February) and vaccine schedule. However, influenza peaks in September in the three states of the Yucatan Peninsula. Influenza-related mortality also peaks in September in Quintana Roo and Yucatan whereas it peaks in May in Campeche. As the current timing of vaccination in Mexico is between October and November, more than half of the annual influenza cases have already occurred in the Yucatan Peninsula states by the time the Northern Hemispheric vaccine is delivered and administered. CONCLUSION: The current Northern Hemispheric influenza calendar adopted for Mexico is not optimal for the Yucatan Peninsula states thereby likely reducing the effectiveness of the immunization of the population. We recommend that Mexico tailor its immunization strategy to better reflect its climatologic and epidemiological diversity and adopt the WHO Southern Hemisphere influenza vaccine and schedule for the Yucatan Peninsula.

A Large Proportion of the Mexican Population Remained Susceptible to A(H1N1)pdm09 Infection One Year after the Emergence of 2009 Influenza Pandemic.

BACKGROUND: The 2009 H1N1 influenza pandemic initially affected Mexico from April 2009 to July 2010. By August 2010, a fourth of the population had received the monovalent vaccine against the pandemic virus (A(H1N1)pdm09). To assess the proportion of the Mexican population who remained potentially susceptible to infection throughout the summer of 2010, we estimated the population seroprevalence to A(H1N1)pdm09 in a serosurvey of blood donors. METHODS: We evaluated baseline cross-reactivity to the pandemic strain and set the threshold for seropositivity using pre-pandemic (2005-2008) stored serum samples and sera from confirmed A(H1N1)pdm09 infected individuals. Between June and September 2010, a convenience sample serosurvey of adult blood donors, children, and adolescents was conducted in six states of Mexico. Sera were tested by the microneutralization (MN) and hemagglutination inhibition (HI) assays, and regarded seropositive if antibody titers were equal or exceeded 1:40 for MN and 1:20 for HI. Age-standardized seroprevalence were calculated using the 2010 National Census population. RESULTS: Sera from 1,484 individuals were analyzed; 1,363 (92%) were blood donors, and 121 (8%) children or adolescents aged ≤19 years. Mean age (standard deviation) was 31.4 (11.5) years, and 276 (19%) were women. A total of 516 (35%) participants declared history of influenza vaccination after April 2009. The age-standardized seroprevalence to A(H1N1)pdm09 was 48% by the MN and 41% by the HI assays, respectively. The youngest quintile, aged 1 to 22 years, had the highest the seroprevalence; 61% (95% confidence interval [CI]: 56, 66%) for MN, and 56% (95% CI: 51, 62%) for HI. CONCLUSIONS: Despite high transmission of A(H1N1)pdm09 observed immediately after its emergence and extensive vaccination, over a half of the Mexican population remained potentially susceptible to A(H1N1)pdm09 infection. Subsequent influenza seasons with high transmission of A(H1N1)pdm09, as 2011-2012 and 2013-2014, are compatible with these findings.

Molecular epidemiology of influenza A/H3N2 viruses circulating in Mexico from 2003 to 2012.

In this work, nineteen influenza A/H3N2 viruses isolated in Mexico between 2003 and 2012 were studied. Our findings show that different human A/H3N2 viral lineages co-circulate within a same season and can also persist locally in between different influenza seasons, increasing the chance for genetic reassortment events. A novel minor cluster was also identified, named here as Korea, that circulated worldwide during 2003. Frequently, phylogenetic characterization did not correlate with the determined antigenic identity, supporting the need for the use of molecular evolutionary tools additionally to antigenic data for the surveillance and characterization of viral diversity during each flu season. This work represents the first long-term molecular epidemiology study of influenza A/H3N2 viruses in Mexico based on the complete genomic sequences and contributes to the monitoring of evolutionary trends of A/H3N2 influenza viruses within North and Central America.

Highly pathogenic avian influenza A(H7N3) virus in poultry workers, Mexico, 2012.

We identified 2 poultry workers with conjunctivitis caused by highly pathogenic avian influenza A(H7N3) viruses in Jalisco, Mexico. Genomic and antigenic analyses of 1 isolate indicated relatedness to poultry and wild bird subtype H7N3 viruses from North America. This isolate had a multibasic cleavage site that might have been derived from recombination with host rRNA.

A (H1N1) pdm09 HA D222 variants associated with severity and mortality in patients during a second wave in Mexico.

BACKGROUND: Pandemic type A (H1N1) influenza arose in early 2009, probably in Mexico and the United States, and reappeared in North America in September for seven more months. An amino acid substitution in the hemagglutinin (HA), D222G, has been reported in a significant proportion of patients with a severe and fatal outcome. We studied the prevalence of HA222 substitutions in patients in Mexico during the second wave and its association with clinical outcome and pathogenicity in a mouse model. METHODS: The nucleotide sequences of hemagglutinin (HA) from viruses collected from 77 patients were determined including 50 severe and fatal cases and 27 ambulatory cases. Deep sequencing was done on 5 samples from severe or fatal cases in order to determine the quasispecies proportion. Weight loss and mortality due to infection with cultured influenza viruses were analyzed in a mouse model. RESULTS: Viruses from 14 out of 50 hospitalized patients (28%) had a non aspartic acid residue at the HA 222 position (nD222), while all 27 ambulatory patients had D222 (p=0.0014). G222 was detected as sole species or in coexistence with N222 and D222 in 12 patients with severe disease including 8 who died. N222 in coexistence with D222 was detected in 1 patient who died and co-occurrence of A222 and V222, together with D222, was detected in another patient who died. The patients with a nD222 residue had higher mortality (71.4%), compared to the group with only D222 (22.2%, p=0.0008). Four of the 14 viruses from hospitalized patients were cultured and intranasally infected into mice. Two viruses with G222 were lethal while a third virus, with G222, caused only mild illness in mice similar to the fourth virus that contained D222. CONCLUSIONS: We confirm the elevated incidence of HA222 (H1N1)pdm09 variants in severe disease and mortality. Both clinical and mouse infection data support the idea that nD222 mutations contribute to increased severity of disease but additional determinants in disease outcome may be present.

Oseltamivir-resistant pandemic (H1N1) 2009 virus, Mexico.

During May 2009-April 2010, we analyzed 692 samples of pandemic (H1N1) 2009 virus from patients in Mexico. We detected the H275Y substitution of the neuraminidase gene in a specimen from an infant with pandemic (H1N1) 2009 who was treated with oseltamivir. This virus was susceptible to zanamivir and resistant to adamantanes and oseltamivir.