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Seasonal Increase in Infectious Diseases Affecting the Respiratory Tract

In the private practice of the SOS Médecins associations (Dijon, Sens, Besançon) in Bourgogne-Franche-Comté, there is typically an increase in activity with the arrival of fall, and starting in mid-September, two main reasons for calls become predominant: respiratory conditions (asthma, bronchiolitis, bronchitis, difficulty breathing, colds, coughs) and flu-like symptoms (fever/sweating, flu, muscle pain, cough). Thus, from week 36 (September 5–11) to week 39 of 2016 (September 26–October 2), calls regarding respiratory conditions rose from 9% to 21% of all calls, and those for flu-like symptoms from 15% to 24%. The third most common reason for calls is gastroenteritis (about 7% of calls).

The increase in calls is fairly consistent from year to year, except for the flu epidemic, which occurs at varying times. This is reflected in an increase in diagnoses related to upper respiratory tract infections (nasopharyngitis, pharyngitis, laryngitis, tracheitis, sinusitis, tonsillitis, otitis) (see Figure 12, page 6). Thus, nasopharyngitis likely reached an initial "winter" peak with 16% of diagnoses in week 38 (September 19–25), based on the previous six years.

Bronchitis is also on the rise, as it is every year (5% of diagnoses from October to March).

The Dijon virology laboratory reports the usual circulation of picornaviruses (rhinoviruses), preceding that of viruses associated with winter epidemics. Based on activity in emergency departments, SOS Médecins associations, and the Sentinelles network over the past six winters: an epidemic phase is expected starting in November for bronchiolitis and starting in December for gastroenteritis, while the epidemic period remains unpredictable for influenza. The peak of each winter epidemic had a very different impact on private practice and hospital activity:

• bronchiolitis accounted for up to 2% of SOS Médecins diagnoses (at the end of the year), but up to 16% for children under 2 years of age, and up to 19% of emergency department diagnoses for children under 2 years of age,

• gastroenteritis accounted for up to 18% of SOS diagnoses (at the start of the year), up to 3% of emergency room visits in Burgundy, and up to 3 cases per 1,000 inhabitants according to the Sentinelles network,

• clinical influenza accounted for up to 30% of SOS diagnoses, but only 2.5% of emergency department activity and up to 7 cases per 1,000 inhabitants according to Sentinelles.

Finally, the autumnal increase in bronchitis cases in SOS activity generally precedes the more winter-typical increase in bronchitis cases treated by emergency departments