key: cord-0001249-byant7dh authors: Gardinassi, Luiz Gustavo; Marques Simas, Paulo Vitor; Salomão, João Batista; Durigon, Edison Luiz; Zanetta Trevisan, Dirce Maria; Cordeiro, José Antonio; Lacerda, Mauricio Nogueira; Rahal, Paula; de Souz, Fátima Pereira title: Seasonality of viral respiratory infections in southeast of Brazil: the influence of temperature and air humidity date: 2012-06-01 journal: Braz J Microbiol DOI: 10.1590/s1517-838220120001000011 sha: 31390ea0f2fc73d3cd3fee80ca0de765ddd68429 doc_id: 1249 cord_uid: byant7dh Viruses are the major cause of lower respiratory tract infections in childhood and the main viruses involved are Human Respiratory Syncytial Virus (HRSV), Human Metapneumovirus (HMPV), Influenzavirus A and B (FLUA and FLUB), Human Parainfluenza Virus 1, 2 and 3 (HPIV1, 2 and 3) and Human Rhinovirus (HRV). The purposes of this study were to detect respiratory viruses in hospitalized children younger than six years and identify the influence of temperature and relative air humidity on the detected viruses. Samples of nasopharyngeal washes were collected from hospitalized children between May/2004 and September/2005. Methods of viral detection were RT-PCR, PCR and HRV amplicons were confirmed by hybridization. Results showed 54% (148/272) of viral positivity. HRSV was detected in 29% (79/272) of the samples; HRV in 23.1% (63/272); HPIV3 in 5.1% (14/272); HMPV in 3.3% (9/272); HPIV1 in 2.9% (8/272); FLUB in 1.4% (4/272), FLUA in 1.1% (3/272), and HPIV2 in 0.3% (1/272). The highest detection rates occurred mainly in the spring 2004 and in the autumn 2005. It was observed that viral respiratory infections tend to increase as the relative air humidity decreases, showing significant association with monthly averages of minimal temperature and minimal relative air humidity. In conclusion, viral respiratory infections vary according to temperature and relative air humidity and viral respiratory infections present major incidences it coldest and driest periods. Brazil is a country where several studies revealed viruses as the main causes of respiratory infections in Fortaleza, in Rio de Janeiro, in São Paulo and in Curitiba (18, 35, 36) , as reported by Arruda et al. (1) . These viruses cause illness that can range from a brief upper respiratory tract infection, as a common cold, to a severe systemic illness, like bronchiolitis and pneumonia, resulting in death (11) . Large countries like Brazil possess a wide range of geographical areas, each one with unique climatic characteristics. Epidemiological studies from tropical regions indicate that factors as rainy seasons (34) or low air humidity (3) , in addition to temperature, may influence respiratory viruses outbreaks. Global warming carries profound changes in Earth´s climate, and major changes in the atmosphere and in the climate have a vast impact on the biosphere and the human environment (20) . Consequently, climatic variations and extreme weather events also cause profound impacts on infectious diseases incidences. Infectious agents (such as protozoa, bacteria and viruses) are devoid of thermostatic mechanisms, and reproduction and survival rates are thus strongly affected by fluctuations in temperature. Temperature dependencies are seen in correlations between disease rates and weather variations over weeks, months or years, as well as in close geographic associations with key climatic variables and the distributions of important infectious diseases (28) . Knowledge of the trends and seasonality of respiratory viral infections in the community could be a first step to confer information for health care providers, to facilitate the implementation of strategies to prevent and minimize transmission, and also introduce early therapeutic options to high risk patients (13) . The aim of this study was to detect the presence of respiratory viruses in clinical samples collected from children with respiratory tract infection, and analyze the seasonal trends and occurrence patterns of the identified viruses. This study was conducted at the Genomic Studies The total respiratory infections were detected mainly in winter, spring and summer of 2004, and autumn and winter of 2005, as showed in Figure 1A , which also demonstrate the seasonal distribution of the detected respiratory viruses. Interestingly, the incidence of viral respiratory infections Results present a significant association between viral respiratory infections and monthly average of minimal relative air humidity (p=0.046) as well as between the monthly average of minimal temperature (p=0.044). Therefore, it was evidenced that meteorological aspects may present influence one over the other, thus temperature tends to fluctuate according to characteristics of relative air humidity while the relative air humidity also varies according to the temperature. In Singapore rates of HRSV disease were associated with higher temperature, lower relative humidity and higher maximal day-to-day temperature variation (3). Weber et al. (1998) described a peak in HRSV-associated ALRI during the rainy season in The Gambia (39); however, earlier studies did not find such an association (15) . Chan and colleagues reported HRSV disease to be directly associated with number of days of rainfall in a month and inversely associated with monthly mean temperature in Malaysia (4). The study, however, did not find an association between HRSV disease and total monthly precipitation (4). On our study HRSV outbreaks presented defined seasonality, occurring in winter, early spring and late autumn periods, being these data similar to previous obtained results (3, 22, 27 Knowledge about HMPV seasonality is limited in Brazil. Despite our results show a low percentage of HMPV detection, they agree with previous reported data (5, 16) showing this virus detection mainly in autumn; however, no significant statistical correlation to variations on temperature or relative air humidity was obtained. The only positive sample to HPIV2 was collected during winter. HPIV1 and HPIV3 detection occurred mainly in late winter and spring. Similar results were reported (5, 26) showing this virus presence in samples collected in spring, autumn and winter. According to literature, HPIV3 are the most frequent viruses from this family, being type 1 and 2 viruses barely detected or even detected, which shows agreement with obtained results to literature data. FLUA and FLUB were detected in few samples; however, these samples were collected during autumn and winter, agreeing to previous studies that showed Inlfuenza outbreaks occurring between late summer and early winter (11, 24, 26) . 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