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Unusually cold, dry weather precedes high pneumonia, flu mortality
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Respiratory infections are more severe during periods of unusual cold or low humidity, even in a subtropical location with typically high humidity, according to a study published in Influenza and Other Respiratory Viruses.
“Reasons for the seasonal pattern in influenza mortality remain unclear,” Robert E. Davis, PhD, professor at the University of Virginia’s department of environmental sciences, and colleagues wrote. “Recent research suggests a connection to weather, particularly cold and/or dry (low humidity) air. Possible explanations for this relationship include factors related to virus characteristics, drying of nasal mucous membranes, enhanced airborne transmission, and human behavioral factors.”
To examine the relationship between weather and influenza and pneumonia mortality, the researchers conducted a retrospective review of data from 1980 to 2009 in Auckland, New Zealand, a humid, subtropical location. The data were collected from the nation’s Ministry of Health.
The researchers acquired data from the National Institute of Water and Atmospheric Research archives, noting morning and afternoon temperatures, as well as dew point temperatures. They specifically examined pneumonia and influenza mortality on unusually cold days, as well as days with low humidity.
Pneumonia and influenza mortality was significantly elevated about 3 weeks after both cold and dry days, results suggested, although the relationship was slightly stronger with temperature than with dew point temperature. Specifically, the data indicated that anomalously cold and dry days were associated with increased pneumonia and influenza mortality. In addition, the researchers found that indoor heating, without humidification, may lengthen survival times of respiratory viruses and weaken nasal defense mechanisms, and that such indoor heating is used most often during abnormally cool weather during the winter, when respiratory infection is most common. The researchers also wrote that people tend to gather in closer proximity during such cold periods, increasing the likelihood of airborne and contact transmission.
“Given the ability to forecast cold and dry periods in advance, such information could potentially be used for ‘real time’ respiratory infection forecasting,” Davis and colleagues wrote. “This could help reduce the impact of pneumonia and influenza in a number of ways: Communication to vulnerable groups (particularly the elderly and those with established respiratory disease), deployment of preventive measures (eg, vaccine and antivirals), and planning for increased service demands in hospitals.” – by Jason Laday
Disclosure: The researchers report no relevant financial disclosures.
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