When the flu season starts varies in different provinces, as do the strains of the viruses
An unseen yet familiar seasonal menace permeates the air we breathe, posing health risks. Acute infectious diseases that affect breathing such as the common cold and Influenza A and B are prevalent during winter.
These diseases occur seasonally and there are some theories for why this happens. The likely theories are that it’s a result of a combination of human behaviour (gathering in spaces with less ventilation), longer viral viability and vulnerability to infection of nasal passages caused by cold air.
Every season varies in terms of the specific strains of viruses in circulation, and determining the precise timing and intensity of the flu season in our country has proven elusive, hindering our ability to respond effectively, allocate healthcare resources and administer vaccinations.
Globally, the flu season, marked by outbreaks of a range of acute respiratory diseases and resulting in up to 650 000 deaths annually, predominantly occurs during the winter months.
When Covid-19 emerged in South Africa, it was at the end of summer, heading into winter, and there was concern that the combined effects of a full winter flu season and the coronavirus would be devastating.
But it turns out the flu season of 2020 was a no-show, mostly because of lockdown, mask-wearing, and other non-pharmaceutical interventions that were put in place to deal with Covid-19. This year, the “tripledemic” of influenza, Covid-19 (yes, still circulating but out of the news), and respiratory syncytial virus infections have caused havoc during the Northern Hemisphere winter.
Working out when flu season is
Our recent study sought to shed light on the fluctuating nature of South Africa’s acute respiratory disease season over the past decade across its nine provinces.
Many countries in the Northern Hemisphere benefit from robust surveillance networks that provide accurate predictions of the season’s commencement. They then disseminate this info to the public and healthcare professionals.
In South Africa the population awaits case reports to assess when the flu season truly begins or ends. To address this knowledge gap, we embarked on a statistical expedition aimed at defining the acute respiratory infectious disease season in our country.
Our analysis involved examining two distinct datasets: public-sector hospital admissions records and private-sector medical insurance claims. These datasets allowed for an exploration of the timing of acute respiratory disease cases throughout the country.
Drawing inspiration from the intensity threshold methodology proposed by the US Center for Disease Control and Prevention in 2017, we tested various thresholds in case and claim numbers to align with the 19-week flu season as defined by the South African National Institute for Communicable Diseases.
Through this analysis, we discovered that each province exhibits distinct thresholds resulting in a 19-week season, albeit with discrete start and end dates. Varying climate zones and socio-economic characteristics probably drive this in the respective provinces.
The findings of this study paint a clearer picture of the acute respiratory infectious disease season in our country. In general, it commences in May, coinciding with the onset of winter, and lingers until September, with the onset of spring.
But the exact week of onset and conclusion varies considerably across the country and from year to year. The characteristics of winter in South Africa also vary across provinces but are generally characterised by cooler temperatures and reduced rainfall in the summer rainfall region (which is most of South Africa).
The different provinces
The Western Cape experiences winter from June to August, which is its rainfall season (unusually wet this year). In the Eastern Cape, winter spans the same period, bringing lower temperatures and increased rainfall with those eastward-moving cold fronts that make it that far.
Gauteng encounters mild to cool conditions with clear skies from about May to August with a wide range of temperatures. KwaZulu-Natal enjoys milder winters from June to August, maintaining moderate temperatures. The Free State grapples with colder winters starting in about May, lasting through to August, and occasionally witnessing snowfall. In the North West, winter commences in May, lasting through to August, with decreased temperatures and occasional frost.
The Northern Cape embraces winter from May to August, characterised by cold temperatures, particularly in high-lying regions where snow may occur. Mpumalanga experiences winter from May to August, encompassing cooler temperatures and sporadic frost in certain areas. Limpopo endures winter from May to August, characterised by cooler temperatures and reduced rainfall.
Acknowledging that these timeframes are approximate and subject to annual variations influenced by weather patterns and climatic conditions is crucial. Global phenomena such as El Niño and La Niña can result in significant variations from the average climate.
The scientific community continues to unravel the intricacies of the timing of respiratory season infections but individual efforts play a pivotal role in safeguarding personal health and the well-being of people.
Remaining vigilant and adopting preventive measures, particularly during the flu seasons, is important. Regular handwashing, covering your mouth and nose when coughing or sneezing, properly disposing of used tissues, using masks in crowded settings and receiving influenza vaccinations are essential in mitigating the risk of contracting and spreading respiratory infections.