The influence of meteorology on the spread of influenza: survival analysis of an equine influenza (A/H3N8) outbreak

• Published in: PloS one Vol. 7; no. 4; p. e35284
• Main Authors: Firestone, Simon M, Cogger, Naomi, Ward, Michael P, Toribio, Jenny-Ann L M L, Moloney, Barbara J, Dhand, Navneet K
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 20-04-2012; Public Library of Science (PLoS)
• Subjects: Aerosols; Air temperature; Ambient temperature; Analysis; Animal populations; Animals; Archives & records; Australia - epidemiology; Biology; Contact Tracing; Coxsackievirus; Data processing; Disease control; Disease Outbreaks; Disease spread; Disease transmission; Empirical analysis; Epidemics; Epidemiology; Foot & mouth disease; Geostatistics; Health hazards; Health risks; Horse Diseases - mortality; Horse Diseases - transmission; Horse Diseases - virology; Horses; Humidity; Immunization; Incubation; Infections; Infectious diseases; Influenza; Influenza A; Influenza A Virus, H3N8 Subtype; Kriging; Kriging interpolation; Laboratories; Medicine; Meteorological conditions; Meteorological data; Meteorology; Mortality; Multivariate Analysis; Orthomyxoviridae Infections - mortality; Orthomyxoviridae Infections - transmission; Orthomyxoviridae Infections - veterinary; Orthomyxoviridae Infections - virology; Outbreaks; Poliomyelitis; Proportional Hazards Models; Rain; Rainfall; Regression analysis; Relative humidity; Risk management; Science; Seasonal variations; Stainless steel; Survival; Survival Analysis; Temperature effects; Veterinary Science; Viral infections; Viruses; Wind; Wind speed; Wind velocities; Australia
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0035284

The influences of relative humidity and ambient temperature on the transmission of influenza A viruses have recently been established under controlled laboratory conditions. The interplay of meteorological factors during an actual influenza epidemic is less clear, and research into the contribution of wind to epidemic spread is scarce. By applying geostatistics and survival analysis to data from a large outbreak of equine influenza (A/H3N8), we quantified the association between hazard of infection and air temperature, relative humidity, rainfall, and wind velocity, whilst controlling for premises-level covariates. The pattern of disease spread in space and time was described using extraction mapping and instantaneous hazard curves. Meteorological conditions at each premises location were estimated by kriging daily meteorological data and analysed as time-lagged time-varying predictors using generalised Cox regression. Meteorological covariates time-lagged by three days were strongly associated with hazard of influenza infection, corresponding closely with the incubation period of equine influenza. Hazard of equine influenza infection was higher when relative humidity was <60% and lowest on days when daily maximum air temperature was 20-25°C. Wind speeds >30 km hour(-1) from the direction of nearby infected premises were associated with increased hazard of infection. Through combining detailed influenza outbreak and meteorological data, we provide empirical evidence for the underlying environmental mechanisms that influenced the local spread of an outbreak of influenza A. Our analysis supports, and extends, the findings of studies into influenza A transmission conducted under laboratory conditions. The relationships described are of direct importance for managing disease risk during influenza outbreaks in horses, and more generally, advance our understanding of the transmission of influenza A viruses under field conditions.