Epidemiological aspects of influenza A related to climatic conditions during and after a pandemic period in the city of Salvador, Northeastern Brazil

Abstract

During the influenza pandemic of 2009, the A(H1N1)pdm09, A/H3N2 seasonal and influenza B viruses were observed to be co-circulating with other respiratory viruses. To observe the epidemiological pattern of the influenza virus between May 2009-August 2011, 467 nasopharyngeal aspirates were collected from children less than five years of age in the city of Salvador. In addition, data on weather conditions were obtained. Indirect immunofluorescence, real-time transcription reverse polymerase chain reaction (RT-PCR), and sequencing assays were performed for influenza virus detection. Of all 467 samples, 34 (7%) specimens were positive for influenza A and of these, viral characterisation identified Flu A/H3N2 in 25/34 (74%) and A(H1N1)pdm09 in 9/34 (26%). Influenza B accounted for a small proportion (0.8%) and the other respiratory viruses for 27.2% (127/467). No deaths were registered and no pattern of seasonality or expected climatic conditions could be established. These observations are important for predicting the evolution of epidemics and in implementing future anti-pandemic measures.

Fig. 1. : virological and climatic data in the city of Salvador, state of Bahia, Brazil, from May 2009-August 2011. Bars represent the influenza (Flu) virus detected. The X-axis shows the years and respective months and the left Y-axis shows the absolute number of positive specimens for influenza viruses (black bars). The right side Y-axis shows the average temperature (ºC), relative air humidity (%) and rainfall (mm x 10). In 2009, the total annual rain volume was 1,176 mm, in 2010, 1,780 mm, and 2011, 1,470 mm.

Fig. 2. : virological and climatic data in the city of Salvador, state of Bahia, Brazil, from May 2009-August 2011. Bars represent the respiratory virus detected. The X-axis shows the years and respective month. The left Y-axis shows the absolute number of positive specimens for respiratory viruses (black bars). The right side Y-axis shows the average temperature (ºC), relative air humidity (%) and rainfall (mm X 10). In 2009, the total annual rain volume was 1,176 mm, in 2010, 1,780 mm, and in 2011, 1,470 mm. RSV: respiratory syncytial virus.