Association between viral seasonality and meteorological factors

Abstract

Numerous viruses can cause upper respiratory tract infections. They often precede serious lower respiratory tract infections. Each virus has a seasonal pattern, with peaks in activity in different seasons. We examined the effects of daily local meteorological data (temperature, relative humidity, "humidity-range" and dew point) from Edinburgh, Scotland on the seasonal variations in viral transmission. We identified the seasonality of rhinovirus, adenovirus, influenza A and B viruses, human parainfluenza viruses 1-3 (HPIV), respiratory syncytial virus (RSV) and human metapneumovirus (HMPV) from the 52060 respiratory samples tested between 2009 and 2015 and then confirmed the same by a generalised linear model. We also investigated the relationship between meteorological factors and viral seasonality. Non-enveloped viruses were present throughout the year. Following logistic regression adenovirus, influenza viruses A, B, RSV and HMPV preferred low temperatures; RSV and influenza A virus preferred a narrow "humidity-range" and HPIV type 3 preferred the season with lower humidity. A change (i.e. increase or decrease) in specific meteorological factors is associated with an increase in activity of specific viruses at certain times of the year.

Figure 1

Comparison of viral seasonality, mean temperature and mean dew point. X axis: Month/Year Y axis: Monthly mean temperature and dew points (shaded area) over the study period and % positivity for each virus (coloured lines, scale differs between viruses). Horizontal line is the average temperature (9.2 °C) across the study period. The line representing the % positivity for each virus demonstrates viral seasonality through the year. It can be compared to the changes in temperature and dew point through the year. In November 2009, HMPV tests were positive 50% of the time, and hence that month’s results are high in comparison to all other results. The high prevalence of rhinovirus and HMPV in 2009 may reflect selective testing for these viruses when the test was introduced.

Figure 2

Comparison of viral seasonality and mean relative humidity. X axis: Month/Year. Y axis: Monthly mean relative humidity (shaded area) over the study period and % positivity for each virus (coloured lines, scale differs between viruses). Horizontal line is the average relative humidity (81%) across the study period. The line representing the % positivity for each virus demonstrates viral seasonality through the year. It can be compared to the changes in mean relative humidity through the year. In November 2009, HMPV tests were positive 50% of the time, and hence that month’s results are high in comparison to all other results. The high prevalence of rhinovirus and HMPV in 2009 may reflect selective testing for these viruses when the test was introduced.

Figure 3

Comparison of viral seasonality and humidity-range. X axis: Month/Year. Y axis: Monthly mean “humidity-range” (shaded area) over the study period and % positivity for each virus (coloured lines, scale differs between viruses). Horizontal line is the average “humidity-range” (25%) across the study period. The line representing the % positivity for each virus demonstrates viral seasonality through the year. It can be compared to the changes in “humidity-range” through the year. In November 2009, HMPV tests were positive 50% of the time, and hence that month’s results are high in comparison to all other results. The high prevalence of rhinovirus and HMPV in 2009 may reflect selective testing for these viruses when the test was introduced.

Figure 4

Generalised Linear Models.The generalised linear models were performed to demonstrate the seasonality of each virus. Using temperature as a comparison meteorological factor, the highest point in the waveform for each virus is the time of year where they are most active in the population 4a: Enveloped viruses in the winter. RSV – 17^th of December, IAV – 12^th of January, IBV – 8^th of February; HMPV – 11^th of March 4b: Non-enveloped viruses. Adenovirus – 5^th of March, Rhinovirus – 6^th of November; 4c: Human parainfluenza viruses. HPIV-1–31^st of October, HPIV-2–15^th of November, HPIV-3–4^th of May.

Figure 5

Change in mean temperature and mean relative humidity as individual viruses increase in activity across a year.Results from ANOVA. Changes in mean temperature and mean relative humidity associated with sequential increase in activity of viruses between January and December (vertical lines - standard error of the mean). Each data point corresponds to the mean temperature or mean relative humidity during the period when the virus is most active (e.g. IAV in January).