Regional Update, Influenza and Other Respiratory Viruses. Epidemiological Week 50 (22 December 2023)

ABSTRACT

[WEEKLY SUMMARY]. North America Influenza activity has reached intermediate levels of circulation in North America and continues to rise. 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 been steadily increasing, reaching elevated levels of circulation in the last four EWs. The activity of SARS-CoV-2 remains at moderate levels, showing stability in 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, associated with a rise 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 influenza cases in the last four EWs. In the United States, a slight increase in influenza activity above the epidemic threshold has been observed, while RSV and SARS-CoV-2 activities remain high. Caribbean Influenza activity has fluctuated at moderate levels in the Caribbean during 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 EWs, has remained fluctuating at moderate levels in the last four EWs. SARS-CoV-2 activity has remained at low levels in the last four EWs. Cases of ILI and SARI have decreased in the last four EWs, with a higher proportion associated with influenza. In Belize, influenza activity has risen in the last three EWs, reaching moderate levels. In the Dominican Republic, RSV activity has maintained a decreasing trend in the last three EWs, reaching moderate levels. In Haiti, SARI activity has fallen below the epidemic threshold with influenza levels around the epidemic threshold. In Jamaica, after a pronounced increase in influenza activity to moderate levels, a slight decrease has been observed in the last EW, below the epidemic threshold, with moderate pneumonia levels. Saint Lucia continues to present elevated levels of SARS-CoV-2 activity. In Barbados, influenza activity remains at intermediate levels with a decrease in the last four EWs, RSV activity continues to decline, and SARS-CoV-2 activity remains at low levels, although showing an increase in the last two EWs. In Guyana, moderate levels have been observed in influenza activity in the last two EWs. Central America Influenza activity, although at low levels, has decreased in the last two EWs in Central America. 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 in the last four EWs and has shown a slight increase in the last three EWs. SARS-CoV-2 activity is at low levels. Although the number of newly detected 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, RSV activity has presented intermediate levels in the last four EWs, SARS-CoV-2 activity has remained low, and influenza activity at epidemic levels has shown a decreasing trend. In Guatemala, RSV activity has decreased in the last four EWs to moderate levels, with a decrease in IRAG cases, mostly positive for RSV. There has also been a slight increase in influenza activity, which has exceeded 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 is at epidemic levels. Although ILI and SARI cases continue to decrease, positive cases for influenza have increased in the last four EWs. In Nicaragua, influenza activity has remained at epidemic levels in the last four EWs, and RSV activity, after reaching a peak of high activity, has started to decrease in the last EW. In Panama, RSV activity continues at elevated levels, while ILI and SARI cases have decreased in the last four EWs, with the majority of positive cases attributable to RSV and SARSCoV- 2. Andean Region Influenza activity has remained stable at low levels of circulation in the Andean region. Over the last four EWs, the predominant influenza viruses have been influenza A(H1N1)pdm09, with circulation to a lesser extent of influenza B/Victoria. RSV activity has remained at low levels. SARS-CoV-2 activity has remained at moderate levels and has been increasing in the last three EWs. ILI activity in the subregion continues at low levels, and SARI cases have shown a slight increase associated with the rise in the proportion of positive cases for influenza in the last four EWs. In Bolivia, SARS-CoV-2 circulation remains high, and SARI cases have remained at epidemic levels in the last EW. In Colombia, SARSCoV- 2, RSV, and influenza activity fluctuate at low levels in the last four EWs. SARI cases also fluctuate around the epidemic threshold, with the majority of positive cases attributable to RSV and, to a lesser extent, influenza. In Ecuador, SARS-CoV-2 has reached high levels, and influenza activity has remained at epidemic-moderate levels in the last four EWs, accompanied by an increase in SARI cases positive for influenza. In Venezuela, influenza activity has fluctuated around the epidemic threshold in the last four EWs. Brazil and Southern Cone Influenza activity remains at low levels of circulation in Brazil and the Southern Cone. 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(H3N2) and influenza A(H1N1)pdm09. RSV activity has remained at low levels. SARS-CoV-2 activity has remained at intermediate-high levels with a slight decrease in the last four EWs. Both SARI and ILI activities have remained low in the last four EWs, with the majority of positive cases attributable to SARS-CoV-2. Argentina has shown moderate SARS-CoV-2 activity with a slight increase in 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, and there is 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 four EWs, with SARI activity at moderate levels, and the majority of positive ILI and SARI cases attributable to SARS-CoV-2. In Uruguay, SARI activity continues to decrease in the last four EWs, with levels below the epidemic threshold, and the majority of positive cases associated with SARS-CoV-2.