Weekly Updates: Influenza, SARS-CoV-2, RSV and other respiratory viruses - Epidemiological Week 37 (22 September 2023)

North America: Influenza activity has remained at low levels. During the last four epidemiological weeks (EWs), the predominant influenza viruses have been influenza A(H1N1)pdm09, with concurrent circulation of influenza B/Victoria. Respiratory syncytial virus (RSV) activity has remained low. SARS-CoV-2 activity continues to rise at moderate levels. Cases of Influenza-Like Illness (ILI) and Severe Acute Respiratory Infection (SARI) continue to increase, with the majority of cases testing positive for SARS-CoV-2. In Mexico, influenza circulation in the last four EWs has remained at epidemic levels, and SARI activity is at moderate levels, with the majority of cases associated with SARS-CoV-2 and to a lesser extent with influenza.

Caribbean: Influenza activity continues to show a decreasing trend in the last four EWs. During this period, the predominant viruses have been influenza B/Victoria, with lesser circulation of influenza A, mainly A(H1N1)pdm09. RSV activity has remained low. SARS-CoV-2 activity has been at intermediate levels of circulation. Cases of ILI and SARI have shown a decreasing trend in the last four EWs. Barbados, Guyana, Jamaica, and Saint Lucia have maintained elevated levels of SARSCoV- 2 circulation.

Central America: Influenza activity continues to decline in the last four EWs. During this period, the predominant influenza viruses have been influenza B/Victoria, with concurrent circulation of influenza A, mainly A(H1N1)pdm09, to a lesser extent. RSV activity has remained elevated in the last four EWs. SARS-CoV-2 activity is at low levels with a decreasing trend. The number of newly detected cases of ILI and SARI has remained low; however, the proportion of SARI cases attributable to RSV remains high. In El Salvador, RSV activity continues to be high, coinciding with an increase in SARS-CoV-2 circulation, which also remains high, as well as, to a lesser extent, with influenza circulation. In Guatemala, in the last four EWs, RSV activity continues to be high, with the majority of ILI and SARI cases testing positive for RSV. In Honduras, after reaching elevated levels in influenza positivity rates, the last four EWs have seen a decline to levels below the epidemic threshold. SARS-CoV-2 activity, following a recent peak in activity, has shown a decreasing trend in the last four EWs. In Nicaragua, influenza activity remains on a declining trend at epidemic levels. In Panama, influenza activity currently remains at epidemic levels, and RSV activity continues to rise, reaching moderate levels.

Andean Region: Influenza activity remains stable at low circulation levels. During the last four EWs, the predominant influenza viruses have been influenza B/Victoria, followed by influenza A, predominantly A(H1N1)pdm09. RSV activity remains low but has shown a slight increase. SARS-CoV-2 remains at moderate levels, with particularly high circulation in Bolivia, a pronounced increase in Ecuador, and a slight increase in Peru. The activity of SARI and ILI continues to decline at low levels.

Brazil and Southern Cone: Influenza activity remains at low circulation levels. During the last four EWs, the predominant influenza viruses have been primarily influenza B/Victoria, with simultaneous circulation of influenza A(H1N1)pdm09. RSV activity remains at low levels. SARS-CoV-2 activity has shown an increase, reaching intermediate levels of circulation. The activity of both SARI and ILI has remained low in the last four EWs. Argentina has seen an increase in SARS-CoV-2 activity, although ILI and SARI levels are below the epidemic threshold. In Brazil, SARS-CoV-2 activity continues to rise. In Chile, a pronounced increase in SARS-CoV-2 activity has also been observed, with intermediate levels of circulation and moderate levels of ILI. In Paraguay, SARI activity has shown a slight increase associated with SARS-CoV-2. In Uruguay, SARI activity continues to decline in the last four EWs, with the majority of cases associated with RSV and, to a lesser extent, SARS-CoV-2.