Regional Update, Influenza and Other Respiratory Viruses. Epidemiological Week 1 (12 January 2024)

ABSTRACT

[WEEKLY SUMMARY]. Regional Situation Over the last four epidemiological weeks (EW), an increase in the activity of Influenza-Like Illness (ILI) has been observed in the Americas region, reaching elevated levels. Concurrently, there has been moderate and stable activity of Severe Acute Respiratory Infection (SARI), associated with both influenza and SARS-CoV-2 positive cases. The rise in ILI activity is mainly linked to increases in North America and Central America, while SARI activity has only increased in North America. Regarding the circulation of respiratory viruses, regional activity of SARS-CoV-2 has been moderate compared to previous epidemic waves. Additionally, there has been an increase in influenza activity, reaching elevated levels considered epidemic for this time of year, along with moderate activity of Respiratory Syncytial Virus (RSV). North America Influenza activity remains at epidemic levels and continues to rise. Over the last four EW, predominant influenza viruses have been A(H1N1)pdm09, with concurrent circulation of influenza B/Victoria and, to a lesser extent, influenza A(H3N2). RSV activity has plateaued over the last four EW at elevated levels. SARS-CoV-2 activity remains moderate to high, showing stability in the last four EW. Cases of ILI and SARI have increased in the last four EW, associated with a rise in the proportion of influenza-positive cases. By country In Canada, SARS-CoV-2 activity has remained high over the last four EW, though showing a decreasing trend. Influenza activity has continued to rise above the epidemic threshold, and RSV activity has remained stable at high levels during this period. In Mexico, influenza circulation has remained stable at epidemic levels in the last four EW, with a decrease in the last EW, and SARI activity remains at moderate levels (with a decrease in the last EW possibly related to underreporting), with the majority of positive cases for influenza in this period. In the United States, the last four EW have shown a stabilization in influenza activity above the epidemic threshold, with a slight decrease in the last EW; RSV and SARS-CoV-2 activity has remained stable at high levels. Hospitalization rates for influenza and SARS-CoV-2 have remained high at similar levels to the previous season, while RSV hospitalization rates have decreased in the last EW. Caribbean Influenza activity has seen a pronounced increase over the last four EW. During this period, predominant viruses have been A(H1N1)pdm09, followed by A(H3N2) and, to a lesser extent, B/Victoria. RSV activity has declined to low levels over the last four EW. SARS-CoV-2 activity has increased in the last four EW, reaching intermediate levels. Cases of ILI and SARI have decreased over the last four EW, with a higher proportion of ILI and SARI cases associated with influenza. By country Elevated influenza activity has been observed in Belize, the Dominican Republic, Barbados, and the Cayman Islands. Elevated SARS-CoV-2 activity has been observed in Jamaica, Saint Lucia, Barbados, the Cayman Islands, and Guyana. Central America Influenza activity has decreased in the last three EW, reaching low levels. Over the last four EW, predominant viruses have been A(H1N1)pdm09 followed by B/Victoria, and to a lesser extent, A(H3N2). RSV activity has remained stable at moderate to high levels over the last four EW. SARS-CoV-2 activity, although remaining at low levels, has increased in the last four EW. Cases of ILI have increased in the last four weeks, with the majority of positive cases attributable to SARS-CoV-2. Cases of SARI have decreased over the last four EW, with a higher proportion of cases associated with SARS-CoV-2. By country In El Salvador, over the last four EW, RSV activity has decreased to low levels, SARS-CoV-2 activity has shown a slight increase but remained fluctuating, and influenza activity has fluctuated around the epidemic threshold. In Guatemala, RSV activity has decreased over the last four EW to low levels, with a corresponding decrease in SARI cases, mostly positive for RSV. There has been a slight increase in influenza activity above the epidemic threshold, coinciding with moderate ILI activity. In Honduras, RSV activity has decreased over the last four EW to low levels, while influenza activity has risen to moderate levels. Although ILI and SARI cases continue to decrease, the majority of positive cases are attributable to influenza. In Nicaragua, influenza activity has remained oscillating around epidemic levels over the last four EW, and RSV activity has remained fluctuating at high levels. In Panama, RSV activity continues at high levels, albeit decreasing, while ILI and SARI cases have increased in the last four EW, with the majority of positive cases attributable to SARS-CoV-2. Andean Region Influenza activity has remained at low levels over the last four EW. During this period, predominant influenza viruses have been A(H1N1)pdm09, with less circulation of B/Victoria. RSV activity has remained at low levels. SARS-CoV-2 activity has been increasing over the last four EW, reaching high levels. ILI and SARI activity in the subregion have remained stable at low levels, with a pronounced increase in the proportion of SARS-CoV-2, influenza, and to a lesser extent, RSV-positive cases among SARI. Most ILI cases have been positive for influenza. By country In Bolivia, SARS-CoV-2 circulation has remained high, and SARI cases have stayed at epidemic levels over the last four EW. In Colombia, SARS-CoV-2, RSV, and influenza activity has remained at low levels, with an increase in the last three EW. SARI cases have remained fluctuating 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 decreasing influenza activity has continued at epidemic levels over the last four EW. This has been accompanied by an increase in SARI cases, with moderate levels, mostly positive for influenza and SARS-CoV-2. In Venezuela, influenza activity has remained fluctuating around the epidemic threshold over the last four EW, with a slight increase in RSV activity. Brazil and the Southern Cone Influenza activity has remained at low circulation levels over the last four EW. During this period, predominant influenza viruses have been A(H3N2) and B/Victoria, followed by A(H1N1)pdm09. RSV activity has remained at low levels. SARS-CoV-2 activity has been increasing at intermediate to high levels over the last four EW. ILI and SARI activity has remained low over the last four EW, with the majority of positive cases attributable to SARS-CoV-2. By country 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 EW. In Brazil, SARS-CoV-2 activity has remained high over the last four EW, with a decreasing trend. In Chile, very high SARS-CoV-2 activity has been maintained, with an increase in influenza activity above the epidemic threshold over the last four EW. ILI cases are at epidemic levels, and SARI cases are below this threshold, mostly attributable to SARS-CoV-2 and, to a lesser extent, influenza. In Paraguay, SARS-CoV-2 circulation has increased over the last four EW to high levels, with SARI activity remaining in decline at epidemic levels, and the majority of positive cases for ILI and SARI attributable to SARS-CoV-2. In Uruguay, SARI activity has continued to decline over the last four EW, remaining below the epidemic threshold, with the majority of positive cases attributable to SARS-CoV-2.