title: Seasonality, timing, and climate drivers of influenza activity worldwide.
abstract: BACKGROUND
  Although influenza is a vaccine-preventable disease that annually causes substantial disease burden, data on virus activity in tropical countries are limited. We analyzed publicly available influenza data to better understand the global circulation of influenza viruses.
  
  
  METHODS
  We reviewed open-source, laboratory-confirmed influenza surveillance data. For each country, we abstracted data on the percentage of samples testing positive for influenza each epidemiologic week from the annual number of samples testing positive for influenza. The start of influenza season was defined as the first week when the proportion of samples that tested positive remained above the annual mean. We assessed the relationship between percentage of samples testing positive and mean monthly temperature with use of regression models.
  
  
  RESULTS
  We identified data on laboratory-confirmed influenza virus infection from 85 countries. More than one influenza epidemic period per year was more common in tropical countries (41%) than in temperate countries (15%). Year-round activity (ie, influenza virus identified each week having ≥ 10 specimens submitted) occurred in 3 (7%) of 43 temperate, 1 (17%) of 6 subtropical, and 11 (37%) of 30 tropical countries with available data (P = .006). Percentage positivity was associated with low temperature (P = .001).
  
  
  CONCLUSIONS
  Annual influenza epidemics occur in consistent temporal patterns depending on climate.
authors: Centers for Disease Control and Prevention, Influenza Division, Atlanta, Georgia 30333, USA. eha9@cdc.gov
authors: Eduardo
authors: E
authors: Azziz Baumgartner
authors: Christine N
authors: CN
authors: Dao
authors: Sharifa
authors: S
authors: Nasreen
authors: Mejbah Uddin
authors: MU
authors: Bhuiyan
authors: Syeda
authors: S
authors: Mah-E-Muneer
authors: Abdullah
authors: A
authors: Al Mamun
authors: M A Yushuf
authors: MA
authors: Sharker
authors: Rashid Uz
authors: RU
authors: Zaman
authors: Po-Yung
authors: PY
authors: Cheng
authors: Alexander I
authors: AI
authors: Klimov
authors: Marc-Alain
authors: MA
authors: Widdowson
authors: Timothy M
authors: TM
authors: Uyeki
authors: Stephen P
authors: SP
authors: Luby
authors: Anthony
authors: A
authors: Mounts
authors: Joseph
authors: J
authors: Bresee
mesh_terms: D002980:Climate; D058872:Epidemics / Q000706:statistics & numerical data*; D014943:Global Health; D006235:Hand Disinfection; D006291:Health Policy; D006801:Humans; D006920:Hygiene; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control; D010353:Patient Education as Topic; D011159:Population Surveillance; D011634:Public Health; D012621:Seasons; D013997:Time Factors; D014611:Vaccination
chemical_list: D007252:Influenza Vaccines