Jude Childrens Research Hospital, Memphis, TN, USA, according to standard methodologies.22 == Statistical analysis == Sample size was calculated using a 95% confidence level and a desired confidence interval of 3%. for the general population was 33.0%, however it was only 24.6% for healthcare workers (p= 0.011). Of the students, 56.6% of those at middle school, 56.4% of those at high school, 52.7% of those at elementary school, and 31.1% of college students showed positive antibodies (p< 0.001). Seroprevalence was 44.6% for college teachers, 31.6% for middle school teachers, and 29.8% for elementary school teachers, but was only 20.3% for high school teachers (p= 0.002). == Conclusions == The student group was the group most affected by influenza A/H1N1/2009, while the healthcare worker group showed the lowest prevalence. Students represent a key target for preventive measures. Keywords:Seroprevalence, Antibodies, A/H1N1/2009, Pandemic influenza, Risk group == Introduction == In April 2009, a new pandemic strain of influenza infected thousands of persons in Mexico and the USA, and spread rapidly throughout the world.1,2A second wave swept through Mexico from October to December 2009. As of July 2010, more than 214 countries worldwide had reported more than 1 million laboratory-confirmed cases of pandemic influenza A/H1N1/2009,3while Mexico had reported 72 548.4However, the true number in Mexico has not yet been determined due to a lack of serological evidence, which might have resulted in an underestimation of the true infection rates in the population. Reasons for under-ascertainment include: asymptomatic cases, not all ill persons seek medical care and have a specimen collected, not all specimens are sent for confirmation with Acamprosate calcium reverse transcription PCR (RT-PCR), and cases of negative results Acamprosate calcium because of the timing of collection or the quality of the specimen.5,6 Most of the estimations of the prevalence of the influenza A/H1N1/2009 pandemic have been performed using indirect measures and predictions, such as multiplier probabilistic models based on laboratory-confirmed cases,7serum cross-reactive antibody responses to infection8or after vaccination with seasonal influenza vaccine,9,10computational approaches,11or estimations derived in other countries from the number of cases imported from Mexico.12,13 Some have identified seroprevalence against pandemic H1N1 in different countries: 32% for children younger than 15 years of age and 20% for those aged 1524 years in England,65.6% in Guangxi Province, Rabbit polyclonal to ZCCHC12 China,921% in Pittsburg, PA, USA,14from 27.7% to 42.8% in Scotland,15and 13% in Singapore.16Other authors have studied particular groups and have found a seroprevalence of 20% in hospital staff in Singapore,17or have measured the antibody response to the pandemic virus resulting from previous influenza infection or vaccination.14,18 Without a direct serological measure, predictions are subject to substantial uncertainty. Direct measurement of the seroprevalence provides valuable information and reliable figures about the epidemiology of the infection, and may be useful in decision-making about transmission models, immunization strategies, and policy-making processes.5,11 No serological studies have been performed in Mexico to assess the seroprevalence of influenza A/H1N1/2009 in groups of people according to the potential risk of transmission. Therefore, this cross-sectional study aimed to identify seroprevalence of antibodies to pandemic influenza A/H1N1/2009 in Acamprosate calcium a large population, separated into groups by potential risk of transmission according to occupation, at the end of the second wave of the pandemic in Mexico. The goal was to provide a direct measure of the incidence of infection in these groups, assessed indirectly by the seroprevalence. == Materials and methods == == Subjects == This was a cross-sectional study of 2222 subjects whose serum samples were collected between November 9 and December 17, 2009 in the metropolitan area of Monterrey, in northeastern Mexico. The region has a population of 2 708 529, including 717 155 students,1940 823 teachers,20and 234.