Effect of climatic conditions on epidemic patterns of influenza in Okinawa, Japan, during the pandemic of 2009: surveillance of rapid antigen test results.
Climatic conditions may have affected the incidence of influenza during the pandemic  of 2009 as well as at other times. This study evaluated the effects of climatic conditions on  influenza incidence in Okinawa, a subtropical region in Japan, during the 2009 pandemic using  surveillance data from rapid antigen test (RAT) results. Weekly RAT results performed in four  acute care hospitals in the Naha region of the Okinawa Islands from January 2007 to July 2011  were anonymously collected for surveillance of regional influenza prevalence. Intense epidemic  peaks were noted in August 2009 and December 2009-January 2010 during the influenza pandemic of  2009. RAT positivity rates were lower during the pandemic period than during the pre- and  post-pandemic periods. Lower ambient temperature was associated with higher influenza incidence  during pre- and post-pandemic periods but not during the pandemic of 2009. Lower relative humidity  was associated with higher influenza incidence during the pandemic as well as during the other two  periods. The association of climatic conditions and influenza incidence was less prominent during  the pandemic of 2009 than during pre- and post-pandemic periods.
Department of Infectious, Respiratory, and Digestive Medicine, Control and Prevention of Infectious Diseases, Faculty of Medicine, University of the Ryukyus, 207 Uehara, Okinawa, Japan.
Yoshikazu
Y
Iha
Futoshi
F
Higa
Satoko
S
Sunagawa
Masamitsu
M
Naka
Haley L
HL
Cash
Kazuya
K
Miyagi
Shusaku
S
Haranaga
Masao
M
Tateyama
Tsukasa
T
Uno
Jiro
J
Fujita
D000956:Antigens, Viral / Q000276:immunology; D002980:Climate; D058872:Epidemics; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology; D009981:Influenza B virus / Q000276:immunology; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology*; D007564:Japan / Q000453:epidemiology; D011159:Population Surveillance
D000956:Antigens, Viral