June 1st, 2009 was an important day in the Nicaraguan Influenza Cohort Study (NICS). Not only did it mark the beginning of the third year of the study, but the first child in the cohort, a 5-year old girl, tested positive for influenza A H1N1pdm on that day. This was the first case detected in the cohort as well as the first case detected in Nicaragua.

Like all countries, Nicaragua moved quickly to prepare for “swine flu” when it was determined that the outbreak of severe respiratory illness in Mexico was due to a new virus, influenza A H1N1pdm. Public health officials and researchers worldwide rapidly moved to monitor the virus as it spread quickly around the world in a matter of weeks. SSI aided Nicaragua in setting up real-time RT-PCR testing for H1N1pdm in the Nicaraguan National Laboratory by sending experts and supplies to the lab in the first week of May. By the time that June 1st rolled around, the National Virology Laboratory had been able to test for several weeks and was well-prepared to diagnose cases as they occurred both in the cohort and in the country.

Between June 1st and October 31st, 177 H1N1pdm cases were detected in the NICS cohort. Because only 25% of children with respiratory symptoms are randomly selected for testing, that number of cases translates into an attack rate of 16.6% in the cohort children. Cases of H1N1pdm are still occurring on a daily basis in the cohort, and it is likely that the attack rate will reach 30-50% by the end of the first year of the pandemic. To date, two cohort study children with laboratory-confirmed H1N1pdm and four children with dual dengue/H1N1pdm virus infections have been hospitalized.

As has been seen with seasonal influenza, many H1N1pdm cases in the cohort have experienced fairly mild symptoms. However, analyses comparing past seasonal influenza cases in the cohort to influenza A H1N1pdm cases have shown that children with H1N1pdm have significantly more lower respiratory symptoms, including more pneumonia in the first week of illness, than children with seasonal influenza. Because the cohort has been ongoing for over two years, we are in a unique position to make these comparisons. In addition to providing invaluable information on how pandemic influenza is affecting children in Central America, the data collected through the study will contribute to overall scientific efforts to understand influenza pandemics.