Regional Update, Influenza and Other Respiratory Viruses. Epidemiological Week 51 (29 December 2023)

ABSTRACT

[WEEKLY SUMMARY]. North America Influenza activity has reached intermediate levels of circulation 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 continued to rise over the last four EWs, reaching high levels of circulation. SARS-CoV-2 activity remains at moderate to high levels, showing stability in the last four EWs. Cases of influenza-like illness (ILI) and severe acute respiratory infection (SARI) have increased over the last four EWs, associated with an increase in the proportion of positive cases for influenza, which has declined in the last two EWs. 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 remains at moderate levels, associated with an increase in the percentage of positive influenza cases in the last four EWs. There has also been an increase in SARI cases requiring ICU admission, primarily associated with influenza and RSV during this period. In the United States, a pronounced increase in influenza activity above the epidemic threshold has been observed, while RSV and SARS-CoV-2 activity has remained at elevated levels with hospitalization rates similar to those observed in the previous season. 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 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. ILI and SARI cases have continued to decline in the last four EWs, with a higher proportion of ILI and SARI cases associated with influenza. In Belize, influenza activity has increased in the last four EWs, reaching moderate levels. In the Dominican Republic, both RSV and influenza activity have maintained a decreasing trend in the last four EWs. In Haiti, SARI activity has fluctuated in the last four EWs, with a decrease in influenza and SARS-CoV-2 activity, reaching above the epidemic threshold in the last EW. In Jamaica, after a pronounced increase in influenza activity to moderate levels, there has been a decline in the last three EWs, falling below the epidemic threshold in the last EW, with moderate pneumonia levels and a slight decrease in the last EW. Saint Lucia continues to present high levels of SARSCoV- 2 activity coinciding with an increase in SARI cases above the moderate activity threshold. Suriname has shown an increase in influenza activity, with SARI activity around the epidemic threshold in the last four EWs. In Barbados, influenza activity has remained on the decline in the last four EWs, reaching low levels, and SARS-CoV-2 activity continues at low levels but showing an increase in the last three EWs. In Guyana, moderate levels of influenza activity have been observed in the last three EWs. Central America Influenza activity remains fluctuating at low to moderate levels 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 shown a pronounced decline in the last two EWs, reaching intermediate levels. SARS-CoV-2 activity is at low levels. Although the number of newly detected cases of ILI and SARI has remained low, the proportion of SARI cases attributable to influenza has increased 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 has oscillated around epidemic levels. In Guatemala, RSV activity has decreased over the last four EWs to intermediate levels, with a simultaneous decrease in SARI cases, mostly positive for RSV. There has also been a slight increase in influenza activity, reaching above the epidemic threshold, coinciding with moderate ILI activity. In Honduras, RSV activity has shown a decline in the last four EWs to low levels, while influenza activity has remained at epidemic levels. Although ILI and SARI cases continue to decline, 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, after reaching a peak of high activity, has started to decline in the last two EWs. In Panama, RSV activity continues at high levels, while ILI and SARI cases have shown a decline in the last four EWs, with most positive cases attributable to RSV and SARS-CoV-2. Andean Region Influenza activity, although remaining at low levels of circulation in the last two EWs, has shown a slight increase. Over the last four EWs, the predominant influenza viruses have been influenza A(H1N1)pdm09, with lesser circulation of influenza B/Victoria. RSV activity has remained at low levels, with a slight increase in the last two EWs. SARS-CoV-2 activity has remained at moderate levels and has been increasing over the last four 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 influenza cases in the last four EWs. In Bolivia, SARS-CoV-2 circulation has remained high, and SARI cases have stayed at epidemic levels in the last four EWs. In Colombia, SARS-CoV-2, RSV, and influenza activity fluctuates at low levels, with a slight increase in the last three EWs, and SARI cases also fluctuate around the epidemic threshold, with most positive cases attributable to RSV and 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. In Venezuela, influenza activity has remained fluctuating around the epidemic threshold in the last four EWs, with a slight increase in RSV activity. Brazil and Southern Cone Influenza activity has remained at low levels of circulation in the last four EWs. During this period, the predominant influenza viruses have been influenza A(H3N2) and influenza B/Victoria, followed by influenza A(H1N1)pdm09. RSV activity has remained at low levels. SARS-CoV-2 activity has remained at intermediate to high levels in the last four EWs. Both SARI and ILI activity have remained low in the last four EWs, with most positive cases attributable to SARS-CoV-2. In Argentina, ILI and SARI levels have remained below the epidemic threshold, with an increase in the percentage of SARS-CoV-2 positivity reaching intermediate levels in the last four EWs. In Brazil, SARS-CoV-2 activity continues at high levels, although with a decrease in the last four EWs. In Chile, SARS-CoV-2 activity has remained very high, with an increase in influenza activity above the epidemic threshold in the last four EWs. ILI cases are at epidemic levels, while SARI cases are below this threshold. In Paraguay, SARSCoV- 2 circulation continues at moderate levels, with an increase in the last four EWs, and SARI activity is decreasing to epidemic levels, with the majority of positive cases of ILI and SARI attributable to SARS-CoV-2. In Uruguay, SARI activity has remained on the