Respiratory syncytial virus seasonality in Brazil: implications for the immunisation policy for at-risk populations

Freitas, André Ricardo Ribas; Donalisio, Maria Rita

All five administrative regions of Brazil were chosen as local of study because they present different socioeconomic and environmental patterns which may influence on virus circulation. The climate in the Midwest region (14, 993, 194 inhabitants) is predominantly tropical, with a rainy season between November and March (monthly rainfall between 13.1-255.6 × 10-3 m) and temperatures ranging 22.0-26.4ºC. The Northeast region (55,794,694 inhabitants) has a semiarid climate in the interior and a tropical Atlantic climate near the coast, where the majority of the population is concentrated, with a monthly rainfall ranging 46.4-281.4 × 10-3 m and a low temperature range (monthly average of 25.1-27.3ºC). The North region (16,983,485 inhabitants) has an equatorial climate with rainfall throughout the year (monthly rainfall between 74.4-303.9 × 10-3 m) and low thermal amplitude (averages 26.3-28.0ºC). The Southeast region (84,465,579 inhabitants) has a predominantly altitude tropical climate with rainfall concentrated between November and March (monthly rainfall between 28.2-285.6 × 10-3 m) and a slightly higher thermal amplitude (monthly average between 18.7-24.6ºC). Finally, the Southern region (28,795,762 inhabitants) has a predominantly subtropical climate with rainfall distributed throughout the year (monthly rainfall between 101.1-198.9 × 10-3 m) and lower temperatures between May and September (monthly average between 14.9-23.1ºC). Influenza sentinel surveillance system data (SIVEP-Gripe) -The laboratory data were obtained from SIVEP-Gripe, which has 128 sentinel surveillance units distributed throughout all the regions of Brazil. The surveillance units record at least five samples of nasopharyngeal secretions weekly from patients with influenzalike illness (measured fever associated with sore throat and/or cough without age group distinction). Samples are processed by using indirect immunofluorescence (IIF), including tests for influenza A and B; parainfluenza 1, 2 and 3; adenovirus; and RSV. The study variables included place of residence, age, and positive and negative IIF results for RSV.