Weekly updates, Influenza Epidemiological Week 28 (21 July 2023)

North America: Influenza activity has remained at low levels. During the last 4 epidemiological weeks (EW), the predominant influenza viruses have been B/Victoria, with a lesser circulation of influenza A (mainly A(H1N1)pdm09). Respiratory syncytial virus (RSV) activity has remained low. SARS-CoV-2 activity has increased in the last 4 EW and continues to circulate at moderate levels. Cases of influenza-like illness (ILI) and severe acute respiratory infection (SARI) continue to show a declining trend, with most of these cases associated with SARS-CoV-2 and, to a lesser extent, influenza.

Caribbean: After an increase in previous weeks, influenza activity has shown a fluctuating trend, now at moderate levels of activity. During the last 4 EWs, the predominant influenza viruses have been B/Victoria, with a lesser circulation of influenza A, mainly A(H1N1)pdm09. RSV activity has remained low. SARS-CoV-2 activity has increased in the recent EWs and is currently at intermediate circulation levels. ILI and SARI cases, after an increase due to positive SARS-CoV-2 and influenza cases in the previous EWs, have shown a decreasing trend in the last 4 EWs.

Central America: After an increase in previous weeks, influenza activity has shown a decline in the last 4 EW, now at moderate circulation levels. During the last 4 EW, the predominant influenza viruses have been influenza A(H1N1)pdm09, with co-circulation, to a lesser extent, of influenza A(H3N2) and influenza B/Victoria. RSV activity has remained low but with a slight increasing trend. SARS-CoV-2 activity has remained low with an upward trend. ILI activity has remained low, with most cases associated with influenza and SARS-CoV-2. SARI activity, although currently declining, showed an increase in the last 4 EWs, with the majority of positive cases attributed to 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; however, ILI and SARI levels have remained low, with most cases associated with influenza and, to a lesser extent, SARS-CoV2. In El Salvador, extraordinary levels of influenza positivity have been reported in the last 4 EWs, but currently, it is declining with moderate levels. In Honduras, after reaching high levels of influenza activity, there has been a decline in the last 4 EWs. Currently, SARI cases are declining, with all positive cases attributed to influenza. In Nicaragua and Panama, following an increase in previous EWs, influenza activity is currently declining at epidemic levels. In Guatemala, there has been an increase in RSV and SARS-CoV-2 activity, with ILI and SARI activity above the epidemic threshold, with most cases being positive for influenza, RSV, and, to a lesser extent, SARS-CoV-2.

Andean region: Influenza activity remains stable at low levels. During the last 4 EW, the predominant influenza viruses have been influenza A, mainly A(H1N1)pdm09, with a lesser circulation of influenza B/Victoria. RSV activity remains at low levels but with an increasing trend. SARS-CoV-2 has shown an increase, circulating at moderate levels. SARI activity, after a slight increase, with most cases associated with influenza and, to a lesser extent, RSV and SARS-CoV-2, is currently declining. 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 EW, the predominant influenza viruses have been mainly A(H1N1)pdm09, with co-circulation of influenza B/Victoria. RSV activity has decreased in the last 4 EW and is now at 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 most SARI cases testing positive for RSV and influenza and most ILI cases testing positive for influenza. In Argentina, an increase in influenza activity has been detected in the last 4 EWs, reaching moderate levels, with most cases detected as positive for influenza A(H1N1)pdm09. After reaching moderate levels of ILI activity, a declining trend has been observed. In Chile, after reaching extraordinary levels of ILI activity, with most cases related to RSV and influenza, this activity has declined in the last 4 EW and is now at epidemic levels. 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. Most of the deaths detected among SARI cases in the last EW have been in cases positive for RSV and, to a lesser extent, SARS-CoV-2. In Paraguay, extraordinary levels of SARI activity continue, with RSV being the main cause among positive cases, followed by influenza, which are currently declining. In Uruguay, after observing an increase in SARI activity, it is currently declining at epidemic levels, with most cases associated with RSV and influenza.