Regional Update, Influenza and Other Respiratory Viruses. Epidemiological Week 46 (24 November 2023) 

ABSTRACT

[WEEKLY SUMMARY]. North America Influenza activity has remained at low levels but is steadily increasing. Over the past 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 intermediate levels compared to previous seasons. 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 increased 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 at epidemic levels with a growing trend 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. Caribbean Influenza activity has fluctuated 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 in previous weeks, has experienced a decline in the last three EWs. SARS-CoV-2 activity continues to decrease, reaching low levels in the last EW. Cases of ILI and SARI have been declining in the last four EWs, with a higher proportion of SARI cases associated with influenza. Belize has experienced a significant decrease in influenza activity in the last two EWs, remaining at moderate levels. The Dominican Republic continues to have elevated RSV activity, although decreasing in the last four EWs. Haiti continues to experience epidemic SARI activity in the last four EWs, with epidemic positivity rates for influenza and a decrease in SARS-CoV-2 to low levels in the last EW. In Jamaica, SARS-CoV-2 activity has slightly increased, accompanied by a pronounced rise in RSV activity in the last four EWs, with epidemic levels of pneumonia and acute respiratory infection. Saint Lucia continues to experience high levels of SARS-CoV-2 activity and an increase in RSV and influenza activity, with declining SARI activity above the moderate activity threshold. In Barbados, influenza activity remains at intermediate and rising levels, RSV activity remains at intermediate levels and has decreased in the last three EWs, while SARS-CoV-2 activity continues to decrease at low levels. Central America Influenza activity, although at low levels, has increased in the last three EWs. Over the last four EWs, the predominant influenza viruses have been influenza B/Victoria, with concurrent circulation of influenza A(H1N1)pdm09 and, to a lesser extent, influenza A(H3N2). RSV activity has remained at moderate to high levels over the last four EWs. SARS-CoV-2 activity is at low levels. Although the number of new ILI and SARI cases detected has remained low, the proportion of SARI cases attributable to RSV has remained high in the last four EWs. In El Salvador, RSV activity has declined to intermediate-low levels, SARS-CoV-2 activity has remained low in the last four EWs, and influenza activity has continued to rise, remaining at epidemic levels in the last two EWs. In Guatemala, RSV activity has decreased in the last four EWs to moderate levels, with a simultaneous decrease in mostly RSV-positive SARI cases and a slight increase in influenza activity, which has surpassed the epidemic threshold. In Honduras, RSV activity has shown a decrease in the last EW, while influenza activity has shown a pronounced increase, reaching moderate levels; SARI cases continue to decline, but positive influenza cases have increased in the last four EWs. In Nicaragua, influenza activity has remained at epidemic levels in the last four EWs, with an upward trend, and RSV activity has continued to rise, reaching intermediate-high levels in this period. In Panama, RSV activity continues at high levels of circulation and is increasing. Andean Region Influenza activity remains at low levels of circulation. Over the last four EWs, the predominant influenza viruses have been influenza A(H1N1)pdm09, followed by influenza B/Victoria. RSV activity fluctuates at low levels. SARS-CoV-2 activity remains at moderate levels, with a slight increase in the last four EWs. SARI and ILI activity in the sub-region continue at low levels. In Bolivia, SARS-CoV-2 circulation remains high, and SARI cases have shown a slight increase, reaching moderate levels in the last EW. In Ecuador, SARS-CoV-2 remains at moderate levels, and influenza activity continues to rise significantly, reaching moderate levels in the last EW. In Colombia, SARS-CoV-2 and RSV activity remain fluctuating at low levels in the last four EWs. In Venezuela, fluctuating levels of influenza activity above the epidemic threshold have been detected, with a decline in the last four EWs. 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 simultaneous circulation of influenza A(H1N1)pdm09 and, to a lesser extent, influenza A(H3N2). RSV activity remains at low levels. SARS-CoV-2 activity has remained constant at intermediate-high levels of circulation in the last four weeks. Both SARI and ILI activity have remained low in the last four EWs, with the majority of positive cases attributable to SARS-CoV-2. Argentina has shown moderate and decreasing SARS-CoV-2 activity over the last four EWs, and influenza activity has shown a slight increase, with ILI and SARI levels below the epidemic threshold. In Brazil, SARS-CoV-2 activity continues to rise, reaching high levels 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, resulting in moderate ILI levels and epidemic levels of SARI in the last four EWs. In Paraguay, SARS-CoV-2 circulation, although low, has shown an increase in the last four EWs, and SARI activity remains at epidemic levels, with most positive cases attributable to SARS-CoV-2. In Uruguay, SARI activity continues to decline in the last four EWs, with levels around the epidemic threshold, with most positive cases associated with SARS-CoV-2, whose positivity rate has decreased in this period.