A recently published paper in Scientific Reports has found that climate variability in the form of the North Atlantic Oscillation (NAO) has had a significant impact on the occurrence of disease outbreaks in Europe over the past fifty years. Researchers in France and the United Kingdom studied 2,058 outbreaks occurring in 36 countries from 114 infectious diseases from 1950 to 2009 and found that climatic variations and seasonal changes in air pressure across the continent attributed to the NAO influenced the outbreak occurrences of eleven diseases. Every conceivable route of transmission – by air, food, water and vector – was influenced by NAO conditions.
The NAO exhibits patterns of air pressure and attendant changes in temperature and precipitation found across western and central Europe and extending across the Atlantic to the eastern North American seaboard. “Strong positive phases of the NAO tend to be associated with above-average temperatures and precipitation across northern and central Europe, and above-average temperatures and below-average precipitation over Mediterranean countries (Southern Europe, North African and Middle-Eastern countries). Opposite patterns of temperature and precipitation abnormalities are typically observed during strong negative phases of the NAO.” The NAO also affects the North Atlantic jet stream, the directionality of hurricanes and, evidently, infectious disease outbreaks.
We know that the weather can affect outbreaks of disease. Autumn brings cooling temperatures and reduced humidity, accompanied by influenza and head colds and congested noses. Food-borne diseases make an appearance during the sizzling temperatures and swampy mugginess of the summer. It’s not just the ambient temperature, precipitation and, apparently, fluctuations in atmospheric pressure that determine the ability of pathogens to survive and propagate in the environment, the weather affects human behavior, our tendencies to venture outside or huddle indoors with our own kind, that too influencing the risk of disease transmission.
For eleven diseases – adenovirus infection, measles, Q fever, aseptic viral meningitis, enterovirus infection, gastroenteritis, typhoid fever, tularaemia, hantavirus infection, hepatitis A and shigellosis – outbreaks in the human population were significantly correlated to the NAO monthly index. Seven were associated with the positive winter phase in northern Europe from November to February. Above-average temperatures and exceptional rainfall resulting from this phase were associated with adenoviruses that cause colds, measles and the diarrheal pathogen Shigella. Incidence of enterovirus and hantavirus in norther Europe were associated with the negative NAO phase in summer and spring respectively, while typhoid spiked with the positive winter phase in southern Europe along with below-average temperatures and rainfall. Hepatitis A took advantage of above-average temperatures and rainfall in southern Europe during the negative winter NAO index.
This is the first such study to examine the link between climate variability and disease outbreaks caused by multiple pathogens and provides compelling evidence for monitoring NAO conditions for the sake of European public health and outbreak control. With this kind of data, monitoring the weather could take an even greater significance and long-term impact than dictating our sartorial choices and plans for outdoor activities: we can begin to look to the skies to gain a picture of the climate of microbes and parasites.
The United Kingdom’s Climatic Research Unit has a simple and informative fact sheet on NAO.
An academic article on the effect of the NAO on the emergence of Atlantic hurricanes.
Morand S, Owers KA, Waret-Szkuta A, McIntyre KM, & Baylis M (2013). Climate variability and outbreaks of infectious diseases in Europe. Scientific reports, 3 PMID: 23639950