A new study investigated the prevalence and transmission of influenza in rural and urban South Africa communities.
The study was conducted by the National Institute for Communicable Diseases (NICD), Perinatal HIV Research Unit (PHRU), WITS Agincourt HDSS in partnership with the US Centers for Disease Control and Prevention (CDC), who also funded the study.
Influenza, a communicable viral disease caused by a spectrum of influenza viruses, affects the upper respiratory tract, including upper and lower respiratory passages. The virus can be transmitted in droplets from coughing, talking or sneezing, and through touching contaminated surfaces.
Researchers enrolled 100 rural and urban households in South Africaeach year and observed them for 10 months. Systematic twice-weekly nasopharyngeal sampling of all household members were conducted, with samples tested by polymerase chain reaction (PCR) for influenza. A total of 81 430 samples were collected from 1116 participants in 225 households, out of which 917 (1%) tested positive for influenza and 79% of households (178/225) had ≥1 influenza-positive individual.
The burden of was high in a rural and an urban African setting, the study revealed, with over three-quarters of households and more than one in three individuals experiencing at least one flu infection each year. It is important to note that the flu incidence risk was similar between the rural and urban areas who participated in the study. The study also showed that recurring flu infections in the same annual flu epidemic, particularly in children, were a common occurrence, accounting for 15% of those infected. Young children also experienced the highest burden of flu infection and symptomatic illness — and compared to other age groups, they were more likely to spread the flu to others in their household.
In addition, the study also revealed that slightly over half of the flu infections were symptomatic. Asymptomatic individuals were also able to spread flu, transmitting the flu to approximately 6% of household contacts. For this reason, authors of the study believe asymptomatic infections to be an important driver of flu transmission.
Medically attended influenza-associated influenza like illness (ILI), defined as a fever and cough as captured by the World Health Organization-recommended flu surveillance programs, suggests the prevalence of flu within communities may be much higher than observed at healthcare facilities. Understanding the community burden and transmission of seasonal influenza is crucial for vaccination programmes and non-pharmaceutical interventions, as well as pandemic preparedness.
In conclusion, the study provides important data on the community burden of flu and transmission thereof in an African setting, a topic that hasn’t been adequately explored. It also contributes important findings relating to symptomatic and asymptomatic flu transmissions, and has implications for the use of non-pharmaceutical interventions and vaccination strategies that target children.
A similar study to examine the burden and transmission of SARS-CoV-2 in the same communities including the role of asymptomatic infections in the spread of SARS-CoV-2 was initiated in July 2020 and results of this study are expected in the coming months.
