Weekly Update: Influenza, SARS-CoV-2, RSV and other respiratory viruses - Epidemiological Week 48 (8 December 2023)

North America: Influenza activity has remained at low levels, although it is on the 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 in the last four EWs, reaching intermediate levels compared to previous seasons. SARS-CoV-2 activity remains at moderate levels, remaining stable 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, 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 cases positive 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 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 continues to decline, reaching low levels in the last three EWs. Cases of ILI and SARI have remained on the decline in the last four EWs, with a higher proportion of SARI cases associated with influenza. In the Dominican Republic, although RSV activity has shown a pronounced decrease in the last four EWs, it remains at medium levels. In Haiti, SARI activity has fallen below the epidemic threshold with influenza levels below that threshold. In Jamaica, a pronounced increase in influenza activity to moderate levels has been observed during the last EW, with moderate pneumonia levels and epidemic levels of Acute Respiratory Infection (ARI). Saint Lucia continues to present elevated levels of SARS-CoV-2 activity coinciding with a sudden increase in SARI activity, which is above the high activity threshold during the last EW. In Barbados, influenza activity remains at intermediate levels with a slight decrease in the last EW, RSV activity remains stable at intermediate levels, and SARS-CoV-2 activity continues at low levels. 

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 at moderate to high levels over the last four EWs. SARS-CoV-2 activity is at low levels. Although the number of new cases detected for 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, during the last four EWs, RSV activity has shown fluctuation at intermediate-low levels, SARS-CoV-2 activity has remained low, and influenza activity has remained fluctuating at moderate levels. In Guatemala, RSV activity has decreased during the last four EWs to medium 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 four EWs to low levels, while influenza activity has shown an increase, reaching epidemic levels. Although cases of ILI and SARI 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, with an upward trend, and RSV activity has continued to rise, reaching intermediatehigh levels in this period. In Panama, RSV activity continues at high levels of circulation and is increasing, while ILI and SARI levels have shown a decrease in the last four EWs, with most positive cases attributable to RSV and SARS-CoV-2. 

Andean Region: Influenza activity has remained stable 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 has remained at low levels. SARS-CoV-2 activity has remained at moderate levels in the last four EWs. SARI and ILI activity in the sub-region continue 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 remain fluctuating at low levels in the last four EWs; however, an increase in SARI cases positive for RSV and, to a lesser extent, influenza has been observed in the last four EWs. In Ecuador, SARS-CoV-2 remains at moderate levels, and influenza activity continues to rise significantly, reaching epidemic levels in the last EW. This has been accompanied by an increase in SARI cases positive for influenza. In Venezuela, fluctuating levels of influenza activity above the epidemic threshold have been detected 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 to a lesser extent of influenza A(H1N1)pdm09 and influenza A(H3N2). RSV activity remains at low levels. SARS-CoV-2 activity has remained constant at intermediate-high levels in the last four EWs. The activity of both SARI and ILI has 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 three EWs, 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 in the last four EWs. In Paraguay, SARS-CoV-2 circulation, although decreasing, continues at moderate levels, with SARI activity at epidemic levels, and most positive cases attributable to SARS-CoV-2. In Uruguay, SARI activity continues to decline in the last four EWs, with levels below the epidemic threshold, with most positive cases associated with SARS-CoV-2, whose positivity rate has decreased in this period.