Weekly updates, Influenza Epidemiological Week 33 (25 August 2023)

North America: Influenza activity has remained at low levels. During the last 4 epidemiological weeks (EW), the predominant influenza viruses have been influenza A(H1N1)pdm09, with concurrent circulation of influenza B/Victoria. Respiratory syncytial virus (RSV) activity has remained at low levels. SARS-CoV-2 activity has shown an increase in the last 4 EW and continues to circulate at moderate levels. Cases of influenza-like illness (ILI) and severe acute respiratory infection (SARI) have shown a slight increase with a rise in the proportion of cases positive for SARS-CoV-2. In Mexico, moderate levels of influenza circulation have been detected in recent EW, however, SARI activity remains low but above the epidemic threshold, with the majority of cases associated with SARS-CoV-2.

Caribbean: Influenza activity continues to show a decreasing trend in the last 4 EWs. During this period, the predominant influenza viruses have been B/Victoria, with lesser circulation of influenza A, mainly A(H1N1)pdm09. RSV activity has remained low. SARS-CoV-2 activity shows an increasing trend with intermediate levels of circulation. ILI and SARI cases have shown a decreasing trend in the last 4 EWs.

Central America: Influenza activity continues to decline in the last 4 EWs. During this period, the predominant influenza viruses have been influenza B/Victoria, with co-circulation of influenza A, mainly A(H1N1)pdm09, and to a lesser extent, influenza A(H3N2). RSV activity has increased in the last 4 EW, reaching medium-high levels of circulation. SARS-CoV-2 activity is at low levels with a decreasing trend. ILI activity has remained low with the majority of cases associated with influenza. SARI activity is currently declining, but the proportion of cases attributable to RSV has increased. In El Salvador, an increase in RSV activity has been observed, coinciding with an increase in SARS-CoV-2 circulation. In Honduras, after reaching elevated levels in influenza positivity rates, the last 4 EW have shown a decrease to levels below the epidemic threshold; however, SARS-CoV-2 activity has increased during this period. SARI cases are currently declining, with almost all positives related to influenza. In Guatemala, RSV activity continues to rise at moderate levels, with moderate levels of ILI and SARI activity; most ILI cases are positive for influenza, and SARI cases are positive for RSV. In Nicaragua and Panama, following moderate activity levels in previous EW, influenza positivity in both countries is currently at epidemic levels. In Panama, RSV activity has increased, reaching moderate levels.

Andean region: Influenza activity remains stable at low levels. During the last 4 EWs, the predominant influenza viruses have been influenza A, predominantly A(H1N1)pdm09, with lesser circulation of influenza B/Victoria. RSV activity remains at low levels. SARS-CoV-2 has shown a decline in the last 4 EWs, circulating at moderate levels, with elevated circulation in Bolivia. SARI activity continues to decline, with the majority of cases associated with influenza and to a lesser extent RSV and SARSCoV- 2. ILI activity has shown a decreasing trend, with most cases associated with influenza.

Brazil and Southern Cone: Influenza activity has decreased to low levels of circulation. During the last 4 EWs, the predominant influenza viruses have been mainly A(H1N1)pdm09, with simultaneous circulation of influenza B/Victoria. RSV activity has decreased in the last 4 EW, reaching low levels of circulation. SARS-CoV-2 activity has remained low. After reaching a peak, both SARI and ILI activity have continued to decline in the last 4 EWs, with the majority of cases being positive for RSV in the case of SARI and influenza in ILI cases. Argentina continues to present epidemic levels of influenza activity, with the majority of cases detected as positive for influenza A(H1N1)pdm09 and ILI and SARI levels below the epidemic threshold. In Brazil, influenza activity is declining, while SARS-CoV-2 has shown a slight increase, with SARI levels above the epidemic threshold, and the majority of cases associated with RSV and to a lesser extent influenza. In Chile, ILI activity remains at moderate levels, with the majority of cases related to influenza. Also, after reaching moderate levels of SARI activity, it is currently declining at epidemic levels, with RSV being the most common cause among positive cases. In Paraguay, SARI activity has decreased, reaching epidemic levels, with RSV as the main cause among positive cases. In Uruguay, SARI activity has decreased in the last EWs, with the majority of cases associated with RSV.