Background There is lack of children disease pattern data on children with 2009 pandemic influenza A(H1N1) in the tropics.

Methods We studied demographics, clinical features, and outcome of Malaysia hospitalised children aged 12 years and below with influenza A (H1N1) from 18^th June 2009 to 1^st March 2010. Real time web electronic case report form was used to collect data. We performed descriptive analysis and ORs with 95% CI were calculated using logistic regression of binary outcome.

Results 1362 children with 2009 pandemic influenza A (H1N1) were hospitalised and 861 (63.2%) were below 5 years. Children below 2 years accounted for over a third (39%) of the patients admitted during the study and almost half (49%) of the mortality. Of the 134 children admitted to the intensive care unit, 101 (75.4%) required mechanical ventilation and 46 (34.3%) died. Pneumonia and acute respiratory distress syndrome was present in 897 (85.5%) and 41 (3.0%) of the hospitalised children respectively including 18 of the 51 (35.3%) non-survivors. The incidence of mortality for children below 12 years, below 5 years and below 2 years, between June through July 2009, was 0.1 per 100 000 corresponding rates between August 2009 through February 2010 was 0.6, 0.9 and 1.3 per 100 000, respectively.

Conclusions The presence of one co-morbid was associated with higher rates of death and relatively a mild disease among hospitalised children in Malaysia.