Weekly Update: Influenza, SARS-CoV-2, RSV and other respiratory viruses - Epidemiological Week 45 (17 November 2023)

North America: Influenza activity has remained at low levels but 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 increase in the last four EWs, reaching intermediate levels compared to previous seasons. SARS-CoV-2 activity remains at moderate levels, showing a slight decrease in 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 remains high but is decreasing, and RSV activity has increased in the last four EWs. In Mexico, influenza circulation has remained at epidemic levels, 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 has been observed, surpassing the epidemic threshold. 

Caribbean: Influenza activity has shown a slight decrease in the last EW but remains at moderate levels. Over the last four EWs, the predominant viruses have been influenza A(H1N1)pdm09, followed by influenza A(H3N2) and, to a lesser extent, influenza B/Victoria. RSV activity has also increased to moderate levels in the last four EWs. SARS-CoV-2 activity continues to decrease, reaching low levels in the last EW. ILI and SARI cases have remained stable in the last four EWs, with a higher proportion of SARI cases associated with SARSCoV- 2 and influenza. Belize has experienced a pronounced decline in influenza activity in the last two EWs, now at moderate levels. The Dominican Republic continues to have elevated RSV activity, although decreasing in the last two EWs. Haiti continues to experience epidemic SARI activity in the last four EWs, with intermediate positivity rates for influenza and SARS-CoV-2. In Jamaica, SARS-CoV-2 activity continues to decrease with low circulation levels, while influenza has increased in the last four EWs, with pneumonia levels above the moderate activity threshold and epidemic levels of acute respiratory infection (ARI) and SARI. Saint Lucia continues to have high levels of SARS-CoV-2 activity and an increase in RSV and influenza activity, with SARI activity above the high activity threshold. In Barbados, influenza activity remains at intermediate levels and is increasing, along with RSV activity in the last EW, while SARS-CoV-2 activity continues to decrease. 

Central America: Influenza activity, although at low levels, has shown a slight increase in the last EW. Over the last four EWs, 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 continued to decrease over the last four EWs, reaching moderate levels. SARSCoV- 2 activity is at low levels. Although the number of new cases of ILI and SARI 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 decreased to intermediate-low levels, SARSCoV- 2 activity has remained low in the last four EWs, and influenza activity has remained at epidemic levels in the last EW. In Guatemala, RSV activity has decreased in the last four EWs to moderate levels, with a corresponding decrease in SARI cases, mostly positive for RSV, and a slight increase in influenza activity, which has reached epidemic levels. In Honduras, RSV activity has remained at moderate levels in the last four EWs, with the majority of SARI cases positive for RSV; influenza activity has increased, reaching epidemic levels in the last four EWs. In Nicaragua, influenza activity has remained at epidemic levels in the last four EWs, and RSV activity has increased in the last two EWs. In Panama, RSV activity continues at high levels and is increasing. 

Andean Region:Influenza activity remains at low circulation levels. Over the last four EWs, the predominant influenza viruses have been influenza A(H1N1)pdm09, followed by influenza B/Victoria. RSV activity remains fluctuating at low levels. SARS-CoV-2 activity is at moderate levels, with a slight increase in the last four EWs. ILI and SARI activity in the subregion remains at low levels. In Bolivia, SARSCoV- 2 circulation remains high, and SARI cases have shown a slight increase, reaching moderate levels in the last EW. In Ecuador, SARSCoV- 2 remains at moderate levels, and influenza activity continues to rise, reaching epidemic levels in the last four EWs. In Colombia, SARS-CoV-2 and RSV activity remain fluctuating at low levels in the last four EWs. In Peru, SARS-CoV-2 activity remains low and is decreasing. In Venezuela, fluctuating levels of influenza activity above the epidemic threshold have been detected, with a decrease in the last four EWs. 

Brazil and Southern Cone: Influenza activity remains at low circulation levels. Over the last four EWs, the predominant influenza viruses have been mainly influenza B/Victoria, with simultaneous circulation of influenza A(H1N1)pdm09. RSV activity remains at low levels. SARS-CoV-2 activity is increasing, with 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 in 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 increase, reaching high levels in the last four EWs. In Chile, very high SARS-CoV-2 activity continues, along 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 increased in the last four EWs, and SARI activity remains at moderate levels, with most positive cases attributable to SARS-CoV-2 in the last four EWs. In Uruguay, SARI activity continues to decrease in the last four EWs, around the epidemic threshold, with most positive cases associated with SARS-CoV-2, which has shown an increase in positivity rates in the last four EWs.