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Influenza A (H1N1) disease burden high among Argentinean children

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Mortality rates attributable to influenza were 10 times higher in Argentinean children compared to those observed during past seasons and hospital rates doubled from 2008, study findings indicated.

The researchers retrospectively compared admission and death rates among 251 children with polymerase chain reaction-confirmed 2009 H1N1 and age-matched children who experienced seasonal influenza in previous years.

Children with 2009 H1N1 were admitted to one-of-six pediatric hospitals in Buenos Aires from May 1 to July 31, which served a catchment area of 1.2 million children.

The researchers determined the following:

• Hospitalization rates among children with influenza were 10.3 per 100,000 in 2008 vs. 20.9 per 100,000 among children with H1N1 in 2009.
• Overall death rates attributable to influenza were 0.1 per 100,000 children with seasonal influenza in 2007 vs. 1.1 per 100,000 among children with 2009 H1N1 (no children died from influenza in 2008).
• Infants experienced the highest death rates at 7.6 per 100,000 (median age 19 months), with most deaths attributable to refractory hypoxemia (62%).
• Increased mortality was associated with a preexisting illness (OR, 4.87%; 95% CI, 1.30-22.23; P=.005), including neurologic disorders (OR, 5.62; 95% CI, 1.13-22.63; P=.003) and chronic lung disease (OR, 3.69; 95% CI, 1.03-13.64; P=.02).

Reported death rates in Argentina were five times that of those reported in the United States during the 2003/2004 influenza season, a year CDC officials considered relatively severe with death rates at 0.2 per 100,000.

“Factors that may have contributed to the high proportion of deaths in Buenos Aires include the rate of chronic medical conditions (69%), delayed consultation or hospital admission, and the unrecognized presentation of 2009 H1N1 influenza,” the researchers wrote.

Infections were also more complicated. In the 2009 influenza season 19% of Argentinean children were admitted to the ICU, 86% required oxygen supplementation, 17% required mechanical ventilation and 5% died. In contrast U.S. population-based studies from earlier influenza seasons revealed that 5% of children were admitted to the ICU, 22% required oxygen supplements and none required mechanical ventilation or died.

Study limitations included a lack of standardization in data recording and clinical evaluation among hospitals and health care providers. The researchers also warned that the scope and magnitude of H1N1 may vary by location, and stated that immunofluorescence assay use during the 2007/2008 season may have resulted in an underestimate of the number of seasonal influenza cases compared with more accurate PCR assays used in 2009.

Libster R. N Eng J Med. 2009;doi:10.1056/NEJMoa0907673.