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Regional Update, Influenza and Other Respiratory Viruses. Epidemiological Week 49 (15 December 2023)

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North America: Influenza activity has reached intermediate levels of circulation and continues to rise. Over the last four epidemiological weeks (EWs), the predominant influenza viruses have been influenza A(H1N1)pdm09, with concurrent circulation of influenza B/Victoria and, to a lesser extent, influenza A(H3N2). Respiratory Syncytial Virus (RSV) activity has continued to rise in the last four EWs, reaching elevated levels of circulation. SARS-CoV-2 activity remains at moderate levels, showing stability over the last four EWs. Cases of Influenza-Like Illness (ILI) and Severe Acute Respiratory Infection (SARI) have shown an increase in the last four EWs, with SARI cases associated with an increase in the proportion of positive cases for influenza. In Canada, SARS-CoV-2 activity has remained high in the last four EWs, with an increase in influenza activity above the epidemic threshold, as well as RSV activity during this period. In Mexico, influenza circulation has remained stable at epidemic levels in the last four EWs, and SARI activity has increased to moderate levels, associated with an increase in the percentage of positive cases for influenza in the last four EWs. In the United States, a slight increase in influenza activity has been observed, surpassing the epidemic threshold. Concurrently, RSV activity is high, and SARS-CoV-2 activity is at moderate levels

Caribbean: Influenza activity has remained fluctuating at moderate levels over the last four EWs. During this period, the predominant viruses have been influenza A(H1N1)pdm09, followed by influenza A(H3N2), and to a lesser extent, influenza B/Victoria. RSV activity, after an increase observed in previous EWs, has remained fluctuating at medium levels during the last four EWs. SARS-CoV-2 activity has remained at low levels in the last four EWs. ILI and SARI cases have decreased in the last four EWs, with a higher proportion of SARI cases associated with influenza. In the Dominican Republic, RSV activity remains at medium levels and, although fluctuating, shows a decreasing trend. In Haiti, SARI activity has fallen below the epidemic threshold with influenza levels around the epidemic threshold. In Jamaica, a pronounced increase has been observed in influenza activity over the last two EWs, reaching moderate levels, with moderate pneumonia levels and epidemic levels of Acute Respiratory Infection (ARI) and SARI. Saint Lucia continues to present elevated levels of SARS-CoV-2 activity, coinciding with a sudden increase in SARI activity above the elevated activity threshold during the last EW. In Barbados, influenza activity remains at intermediate levels, with a decline in the last two EWs, RSV activity is decreasing, and SARS-CoV-2 activity continues at low levels, although showing an increase in the last two EWs. 

Central America: Influenza activity, although at low levels, has shown an increase in the last four EWs. During this period, the predominant influenza viruses have been influenza B/Victoria, with concurrent circulation, to a lesser extent, of influenza A(H1N1)pdm09 and influenza A(H3N2). RSV activity has remained high during the last four EWs and has shown a slight increase in the last two EWs. SARS-CoV-2 activity is at low levels. Although the number of new ILI and SARI cases has remained low, the proportion of SARI cases attributable to RSV has remained high in the last four EWs. In El Salvador, during the last four EWs, RSV activity has shown an increase at intermediate levels, SARS-CoV-2 activity has remained low, and influenza activity at epidemic levels has shown a decreasing trend. In Guatemala, RSV activity has decreased over the last four EWs to medium levels, with a decrease in SARI cases, mostly positive for RSV. There has also been a slight increase in influenza activity, surpassing the epidemic threshold, coinciding with moderate ILI activity. In Honduras, RSV activity has shown a decrease in the last four EWs to low levels, while influenza activity has shown an increase, reaching epidemic levels. Although ILI and SARI cases continue to decrease, positive influenza cases have increased in the last four EWs. In Nicaragua, influenza activity has remained at epidemic levels in the last four EWs, and RSV activity has continued to rise, reaching high levels in this period. In Panama, RSV activity continues at high levels, while ILI and SARI levels have decreased in the last four EWs, with most positive cases attributable to RSV and SARS-CoV-2. viruses have been influenza A(H1N1)pdm09, followed by influenza B/Victoria. 

RSV activity has remained at low levels. SARS-CoV-2 activity has remained at moderate levels in the last four EWs. ILI and SARI activity in the subregion continues at low levels, although an increase in the proportion of SARI cases positive for influenza has been observed. In Bolivia, SARS-CoV-2 circulation continues to be high, and SARI cases have remained at epidemic levels in the last EW. In Colombia, SARS-CoV-2, RSV, and influenza activity fluctuate at low levels in the last four EWs. SARI cases also fluctuate around the epidemic threshold, with most cases positive for RSV and, to a lesser extent, influenza. In Ecuador, SARS-CoV-2 has reached high levels, and influenza activity has remained at epidemic levels in the last four EWs, accompanied by an increase in SARI cases positive for influenza. 

Brazil and Southern Cone: Influenza activity remains at low levels of circulation. Over the last four EWs, the predominant influenza viruses have been mainly influenza B/Victoria, with concurrent circulation, to a lesser extent, of influenza A(H1N1)pdm09 and influenza A(H3N2). RSV activity has remained at low levels. SARS-CoV-2 activity has remained at intermediate to high levels, with a slight decrease in the last four EWs. ILI and SARI activity have remained low in the last four EWs, with most positive cases attributable to SARS-CoV-2. Argentina has presented moderate SARS-CoV-2 activity with a slight increase during the last four EWs, with ILI and SARI levels below the epidemic threshold. In Brazil, SARS-CoV-2 activity continues at high levels, although with a decrease in the last four EWs. In Chile, very high SARS-CoV-2 activity continues to be observed, with an increase in influenza activity above the epidemic threshold. In Paraguay, SARS-CoV-2 circulation continues at moderate levels, showing an increase in the last two EWs, with SARI activity at epidemic levels and most positive cases attributable to SARS-CoV-2. In Uruguay, SARI activity continues to decrease in the last four EWs, with levels below the epidemic threshold, with most positive cases associated with SARS-CoV-2.