Pandemic A(H1N1) 2009 influenza: review of the Southern Hemisphere experience.

We sought to systematically review the published literature describing the epidemiological aspects of the first wave of pandemic A(H1N1) 2009 influenza in the Southern Hemisphere. Fifteen studies were included in this review, originating from South America, Australia or New Zealand, and Africa. Across the different studies, 16·8-45·3% of the laboratory-confirmed cases were admitted to hospital, and 7·5-26·0% of these cases were admitted to intensive care units (ICUs). The fatality rate was 0·5-1·5% for laboratory-confirmed cases in 6/8 studies reporting specific relevant data, and 14·3-22·2% for cases admitted to ICUs in 5/7 studies, respectively. In 4/5 studies the majority of laboratory-confirmed cases were observed in young and middle-aged adults, the percentage of older adults increased the higher the level of healthcare the cases received (e.g. laboratory confirmation, hospitalization or ICU admission) or for fatal cases. Many of the cases had no prior comorbidity, including conditions identified as risk factors for seasonal influenza. Pregnant women represented 7·4-9·1% and 7·1-9·1% of unselected laboratory-confirmed cases and of those admitted to ICUs, respectively. Obesity and morbid obesity were more commonly reported as the level of healthcare increased.