In many places, influenza activity peaks during the period in between December and February. What are some of the best practices to reduce the spread of the flu and to minimize the risk of catching it? The standard recommendations are: get a flu shot if you are in a risk group, cough and sneeze into your elbow and wash your hands frequently. On an individual basis, we can follow these recommendations and hope for the best outcomes. From a public health standpoint, it is a good idea to understand how a flu outbreak starts. A recent article published in the Journal of Clinical Virology gives insight in this regard.
Researchers at Sahlgrenska Academy in the University of Gothenburg in Gothenburg, Sweden conducted the study during the period between October 2010 and July 2013. During that period, researchers collected more than 20,000 nasal swabs from people seeking medical care in and around the city of Gothenburg, and analyzed them for influenza A and other respiratory viruses.
The incidence of respiratory viruses was then compared over time with weather data from the Swedish Meteorological and Hydrological Institute (SMHI). The findings: Flu outbreaks seem to be activated about one week after the first really cold period with low outdoor temperatures and low humidity.
The finding of this study has been reported in Time.com. Here are the abstracts of the study in three different places (here, here and here) for anyone who would like more detailed information. Here is the press release from the Sahlgrenska Academy.
The most interesting take away from the study is the predictable timing with the flu outbreak starting the week after a cold snap. There is a lag time of about a week. The onset of a cold snap is a leading indicator of a flu outbreak. The correlation is a useful piece of information.
If you know when the cold month begins, you know when the flu activity starts to get intense. Thus this knowledge can be put to good use. For example, start publicize the need for flu shots in the period leading to the first cold month. It can also help hospitals and other health providers prepare in advance for a higher volume of patients seeking care.
Even individuals can make use of this insight. In the period leading to the first cold spell, be extra careful and take extra precaution: hand washing and sneezing into elbow for example.
Cold temperature and dry weather condition together allow the flu virus to spread more easily. According to the study, aerosol particles containing virus and liquid are more able to spread in cold and dry weather. The dry air absorbs moisture and the aerosol particles shrink and can remain airborne.
Of course, the cold and dry weather alone is not enough to cause an outbreak of the flu. According to one of the researchers, “the virus has to be present among the population and there have to be enough people susceptible to the infection.”
The study indicates that the findings for seasonal flu (Influenza A) also hold true for a number of other common viruses that cause respiratory tract infections, such as RS-virus and coronavirus. The combination of cold and dry weather seems to exacerbate the problems caused by these viruses. On the other hand some viruses such as rhinovirus, that are a common cause of cold, are independent of weather factors and is present all year round.