Influenza cases at sentinel influenza-like illness (ILI) and pneumonia surveillance sites have been steadily increasing since week 15 (starting 10 April 2023) (figure 1). Private laboratories have also detected increasing numbers of influenza cases, and NICD has received reports of influenza clusters in schools and workplaces.

The 2023 influenza season started in week 17 (week starting 27 April 2023) when the influenza detection rate (3-week moving average) breached the seasonal threshold and remained on low activity for two consecutive weeks in the pneumonia surveillance programme. The increase in case numbers has been identified in all 6 provinces where surveillance is conducted. As of 28 May 2023, the most commonly detected subtype and lineage is influenza A (H3N2) (146/272, 55%), followed by influenza A (H1N1)pdm09 (116/272, 43%) and, influenza B Victoria (3/272, 1%). 181 samples have subtyping results pending.

Influenza A(H3N2), A(H1N1)pdm09, and influenza B are common seasonal influenza strains in humans. Influenza A(H1N1)pdm09, which is sometimes incorrectly referred to as “swine flu” has been one of the circulating seasonal influenza strains following its emergence in 2009. The term “swine flu” should not be used as it causes unnecessary panic. The clinical course of infection and management of this strain is similar to other influenza strains.

Although the majority of people with influenza will present with mild illness, influenza may cause severe illness, which may require hospitalisation or cause death, especially in individuals who are at risk of getting severe influenza illness or complications. Groups at increased risk of severe illness or complications of influenza include pregnant women, people living with HIV, people with chronic illnesses or conditions like diabetes, lung disease, tuberculosis, heart disease, renal disease and obesity, the elderly (65 years and older) and children less than 2 years old. These groups should be encouraged to seek medical help early.

As the influenza season has started, the influenza vaccine remains the primary means for preventing seasonal influenza infection. Ideally, the vaccine should be administered before the influenza season (March to April). However, even if the season has already started, it is never too late to get vaccinated, especially for individuals who have high risk of severe influenza illness or complications. To prevent contracting or spreading the influenza virus,  the following measures are recommended: avoid close contact with sick individuals, stay home when sick, cover mouth and nose when coughing or sneezing, regularly clean hands, avoid touching the mouth, eyes, and nose, and clean and disinfect commonly used surfaces. Clinicians should include influenza as a possible diagnosis when managing patients with respiratory illness.

Updated guidelines on influenza diagnosis and management are available at: https://www.nicd.ac.za/wp-content/uploads/2023/05/Influenza-guidelines_-25April-2023-final.pdf 

Weekly influenza surveillance reports are published at:

https://www.nicd.ac.za/diseases-a-z-index/disease-index-covid-19/surveillance-reports/weekly-respiratory-pathogens-surveillance-report-week/