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Pediatric Hospitalizations Due to Influenza in 2010 in Argentina

Much concern has been raised about the upcoming 2010–2011 flu season in the Northern Hemisphere. In preparation for this event, we investigated the burden of influenza during the 2010 season in the Southern Hemisphere in the same hospitals involved in our report in the Journal (Jan. 7 issue)1 of serious disease in children in Argentina during the 2009 season.

During 2009, Argentina had the third largest number of deaths due to pandemic influenza in the Americas.2 As reported in the Journal, 1 our retrospective case series consisted of 251 hospitalizations and 13 deaths between May 1 and July 31, 2009, in a catchment population of 1.2 million children. The hospitalization and death rates of 20.9 and 1.1 per 100,000 children, respectively, exceeded rates due to seasonal influenza viruses in previous years by a factor of 2 and a factor of 10, respectively.

From May 1 to July 31, 2010, we evaluated the burden of illness caused by the 2009 pandemic influenza A (H1N1) virus in five of the six pediatric institutions surveyed in 2009.1 The study was approved by the institutional review boards of the participating institutions. The sixth hospital transiently interrupted testing for pandemic flu during this season and was therefore excluded from our analysis. The five hospitals included provide medical care for a population of approximately 900,000 children. The evaluation period was chosen on the basis of flu seasonality in previous years.1,3 Assessment for pandemic influenza was performed by testing nasal aspirates or both nasal and throat swabs with the use of a real-time reverse-transcriptase–polymerase-chain-reaction assay.1 No pediatric hospitalizations due to 2009 H1N1 influenza were identified (P<0.001 for the comparison with the 2009 season). In all, 42 children were hospitalized because of influenza B, and 1 child because of influenza A (H3N2). Three children infected with influenza B who also had chronic lung disease recovered after intensive care.

Several factors most likely contribute to the apparent absence of severe pediatric cases of 2009 H1N1 influenza in Argentina during the recent influenza season. First, uptake or administration of the influenza A (H1N1) 2009 monovalent vaccine in infants, children under 5 years of age, and children with high-risk medical conditions was 93% before this season.3 In the previous season, this group accounted for 98% of admissions.1,4 In addition, the availability and use of oseltamivir may have contributed to the lessening of severe presentations. Oseltamivir was not widely available in Argentina early in 2009.1 Finally, an estimated one child in every three acquired the 2009 H1N1 virus during that year, leaving many protected during the subsequent season.5

Although additional surveillance data from other countries are needed, these data from Argentina suggest that the severity of the upcoming 2009 H1N1 season in the Northern Hemisphere may be diminished.

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