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Why do we catch cold and flu during winter?

Wintertime is usually associated with increased risks of upper and lower respiratory tract infections:

  • Most respiratory viruses, including rhinoviruses and influenza show a peak in winter, especially in children (1)
  • Upper respiratory tract infections such as common cold, throat infection, pharyngitis, rhino-sinusitis etc. account for 30-40% of general practice consultations each year (2)
  • In September 2017, the head of NHS England has warned hospitals and GP surgeries to be prepared for a big increase in cases of flu this winter (3)
  • 82% of chronic bronchitis occur during fall and winter (4)
  • People with chronic pulmonary diseases show an almost two-fold increase of exacerbations in the winter months (5)
  • In asthmatic adults, there is a peak of virus-triggered exacerbations in the winter (6)

But why ?

“Cover yourself up or you’ll catch a cold!” The association between wintertime and colds and flu is popular knowledge, but the reasons are not always well understood. First, it can be linked to the cold itself, and the fact cold temperatures lead to drier air, which may dehydrate mucosa, preventing the body from effectively expelling pathogens. It is also hypothesized that certain viruses survive longer on surfaces at colder temperatures and aerosol transmission is highest in cold environments (under 5 °C) with low relative humidity. Another reason is behavioural: people tend to spend more time indoors, in crowded spaces, they are in close contact more often, increasing the risk of transmission.

Seasonality of influenza virus showing clear winter peaks (7)

  1. Ramaekers K. et al. (2017). Prevalence and seasonality of six respiratory viruses during five consecutive epidemic seasons in Belgium. J Clin Virol. 2017 Sep;94:72-78
  2. Ashworth M, Latinovic R, Charlton J, Cox K, Rowlands G, Gulliford M. Why has antibiotic prescribing for respiratory illness declined in primary care? A longitudinal study using the General Practice Research Database. J Public Health 2004;26:268e74.
  3. NHS is warned to be on high alert for flu this winter.BMJ 2017 Sep 13;358:j4284.
  4. Macfarlane J, Holmes W, Gard P et al. Prospective study of the incidence, aetiology and outcome of adult lower respiratory tract illness in the community.  Thorax, 2001 Feb;56(2):109-14
  5. Jenkins CR, Celli B, Anderson JA et al. Seasonality and determinants of moderate and severe COPD exacerbations in the TORCH study. Eur Respir J. 2012 Jan;39(1):38-45
  6.  Guilleminault L et al. Seasonality in asthma: Impact and treatments. Presse Med. 2016 Nov;45(11):1005-1018.
  7. Visseaux B et al. Prevalence of respiratory viruses among adults, by season, age, respiratory tract region and type of medical unit in Paris, France, from 2011 to 2016. PLoS One, 2017 Jul 14;12(7):e0180888.