Global Influenza Hospital-based Surveillance Network (GIHSN): results of surveillance of influenza and other respiratory viruses in hospitalised patients in Brazil, 2015

Raboni, Sonia M; Moura, Fernanda EA; Caetano, Braulia C; Avanzi, Valéria M; Pereira, Luciane A; Nogueira, Meri B; Vidal, Luine R; Tavares, Isabel CF; Pradel, Florence K; Picot, Valentina S; Puig-Barbera, Joan; Siqueira, Marilda M

Epidemiological results revealed variations in the peak time of influenza infections between Northeast (Fortaleza) and South (Curitiba) Brazil, which basically followed the rain period of each region. In the Northeast, in particular, viral circulation was prevalent in the first 4 months of the year, indicating that the vaccination campaign was being carried out in a post)seasonal period, possibly explaining the low effectiveness. The main weakness of the data is the low inclusion of patients in Rio de Janeiro that does not allow for an assessment of the impact of viral respiratory infections in southeastern Brazil. Seasonal influenza epidemics peak during the winter in temperate latitudes of both the Northern and Southern Hemispheres. In contrast, tropical countries may experience two annual peaks, with shorter and less intense epidemics. [3, 4] Moreover, previous studies showed that influenza activity has been frequently out of phase with the hemispheric winter in many tropical regions, and even temperate ones, with the consequence that optimal timing for routine influenza vaccination recommendations does not necessarily correspond to the one expected for their hemisphere. [5] . In Brazil, which presents temperate and tropical regions, it has been showed an important regional heterogeneity in influenza peak. [6, 7] Besides climate and environmental conditions, which have shown an association between seasonal influenza epidemics with "cold)dry" and "humid)rainy". [ In Fortaleza, the study was conducted at HIAS, a public health institution of 270 beds. It is a city of 2,500,000 inhabitants at sea level, 4° south of the equator. Its tropical climate is characterized by two distinct seasons: a rainy one between January and May, and a dry one during the rest of the year. There is high relative humidity (79%) and little variation in the average temperature (26.4°C).