Weekly updates, Influenza Epidemiological Week 29 (28 July 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 low. SARS-CoV-2 activity has shown an increase in the last 4 EWs and continues to circulate at moderate levels. Cases of influenza-like illness (ILI) and severe acute respiratory infection (SARI) have remained at low levels, with the majority of these associated with SARS-CoV-2 and to a lesser extent influenza. In Mexico, moderate levels of influenza circulation have been detected in the last EWs; however, the activity ILI and SARI remains low but above the epidemic threshold.

Caribbean: After an increase in previous weeks, influenza activity has shown a decreasing trend in the last 4 EWs. During the last 4 EWs, 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 has shown an increase in the last 4 EWs and currently remains at intermediate levels of circulation. Cases of ILI and SARI, after an increase due to positive cases of influenza and SARS-CoV-2 in previous EWs, have shown a decreasing trend in the last 4 EWs.

Central America: Influenza activity, after reaching a peak in previous weeks, has shown a decline in the last 4 EWs. During the last 4 EWs, the predominant influenza viruses have been influenza A, mainly A(H1N1)pdm09, with concurrent circulation of influenza B/Victoria and influenza A(H3N2) to a lesser extent. RSV activity has shown an increase in the last 4 EWs, reaching intermediate levels of circulation. SARS-CoV-2 activity has remained low. ILI activity has remained low, with the majority of cases associated with influenza and SARS-CoV-2. SARI activity is currently declining, with the majority of cases associated with influenza and to a lesser extent RSV and SARS-CoV-2. In Costa Rica, extraordinary levels of influenza positivity have been observed, coinciding with concurrent circulation of SARS-CoV-2, showing a decline for both in the last 2 EWs, with low ILI and SARI levels, with the majority of cases associated with influenza and to a lesser extent SARS-CoV-2. In El Salvador, extraordinary levels of influenza positivity have been reported in the last 4 EWs, although currently in decline, with epidemic levels in reported SARI cases. Additionally, an increase in RSV positivity levels has been observed with elevated activity. In Honduras, after reaching high percentages of influenza positivity, a decline has been observed in the last 4 EWs. SARI cases are currently declining, with all positives related to influenza. In Guatemala, after an increase in RSV activity, a decline has been observed in the last 4 EWs, with moderate levels of ILI and SARI activity, with cases mostly positive for influenza and RSV. In Nicaragua and Panama, after moderate activity levels reached in previous EWs, influenza positivity in both countries is currently declining at epidemic levels.

Andean region: Influenza activity remains stable at low levels. During the last 4 EWs, the predominant influenza viruses have been influenza A, mostly A(H1N1)pdm09, with lesser circulation of influenza B/Victoria. RSV activity, although showing a slight increase, remains at low levels. SARS-CoV-2 continues to circulate at moderate to high 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 SARS-CoV-2. ILI activity has shown a decreasing trend, with the majority of cases associated with influenza.

Brazil and Southern Cone: Influenza activity has decreased to low circulation levels. 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 shown a decline in the last 4 EWs, reaching low circulation levels. 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 positive for RSV and influenza in the case of SARI and influenza in ILI cases. In Argentina, a pronounced increase in influenza activity has been observed in the last 4 EWs, reaching elevated levels, with the majority of cases detected as positive for influenza A(H1N1)pdm09, and after reaching moderate activity levels for ILI, it is currently declining. In Chile, after reaching extraordinary levels of ILI activity, with the majority of cases related to RSV and influenza, this activity has declined in the last 4 EWs, currently at epidemic levels. Also, after reaching moderate activity levels for SARI, it is currently declining at epidemic levels, with RSV being the most common cause among positive cases. The majority of deaths detected among SARI cases in the last EW have been positive for RSV and to a lesser extent for SARS-CoV-2. In Paraguay, extraordinary levels of SARI activity continue, with RSV being the main cause among positive cases. In Uruguay, an increase in SARI activity has been detected in the last 4 EWs, continuing at moderate levels, with the majority of cases associated with RSV and influenza.