Somasundram Pillay
Background and study aim: Respiratory tract infections cause substantial morbidity, and multiplex polymerase chain reaction (PCR) testing demonstrates concurrent circulation of multiple respiratory pathogens. National data describing temporal co-circulation patterns in South Africa remain limited. The aim was to characterise seasonal temporal co-circulation and assess whether pathogen activity shows non-random population-level associations in South Africa during 2024.Patients and methods: Public respiratory surveillance reports from Ampath and Lancet Laboratories (January–December 2024) were analysed using monthly percentage positivity. Pathogens included respiratory viruses (influenza A/B, respiratory syncytial virus, rhinovirus/enterovirus, SARS-CoV-2, adenovirus, parainfluenza, bocavirus, human metapneumovirus) and atypical bacteria (Mycoplasma pneumoniae, Chlamydophila pneumoniae, Bordetella pertussis). Co-circulation was defined as ≥2 pathogens exceeding 10% positivity in the same month. Temporal trends and seasonal clustering were examined descriptively.Results: Rhinovirus/enterovirus predominated year-round (peak 33.9% in February). Influenza A peaked in May (41.5%) and influenza B in August (19.8%). Respiratory syncytial virus peaked in March (21.2%), while human metapneumovirus increased in September–November (≥10%). Co-circulation occurred in 7 of 12 months; rhinovirus/enterovirus most often overlapped with influenza A, respiratory syncytial virus, and human metapneumovirus, while influenza A and B did not co-circulate above threshold. Atypical bacterial pathogens were detected at low frequencies but did not reach the positivity cut-off required to identify dominant circulating pathogens. Co-circulation was more frequent in winter months and during periods of influenza A or human metapneumovirus activity.Conclusion: Respiratory pathogen activity in 2024 was seasonally structured and non-random, supporting multiplex testing and anticipatory surveillance for periods of increased pathogen co-circulation.