Regional Update, Influenza and Other Respiratory Viruses. Epidemiological Week 52 (5 January 2024)

ABSTRACT

[WEEKLY SUMMARY]. Regional Situation Over the past four epidemiological weeks (EWs), an increase in Influenza-Like Illness (ILI) activity has been observed in the Americas region, reaching elevated levels. Concurrently, there has been a moderate and stable activity of Severe Acute Respiratory Infection (SARI), both associated with positive cases of influenza and SARS-CoV-2. The rise in ILI activity is mainly linked to increases in North America and Central America, while SARI activity has only seen an increase in North America. Regarding the circulation of respiratory viruses, the regional SARS-CoV-2 activity 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 EWs, the 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 EWs with elevated circulation levels. SARS-CoV-2 activity continues at moderate to high levels, remaining stable in the last four EWs. Both ILI and SARI cases have shown an increase in the last four EWs, associated with a rise in the proportion of positive cases for influenza. By countries 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 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 (with a decrease in the last EW, possibly related to underreporting), showing an increase in the percentage of positive cases for influenza during this period. In the United States, a pronounced increase in influenza activity above the epidemic threshold has been observed in the last four EWs. The activity of RSV and SARS-CoV-2 has remained stable at high levels. Hospitalization rates for influenza and SARS-CoV-2 continue to rise at similar levels to the previous season, while hospitalization rates for RSV have declined in the last two EWs. Caribbean Influenza activity has remained at moderate levels over the last four EWs. During this period, the predominant viruses have been A(H1N1)pdm09, followed by A(H3N2) and, to a lesser extent, B/Victoria. RSV activity, after an increase in previous EWs, has remained in decline to low levels over the last four EWs. SARS-CoV-2 activity has increased in the last two EWs, reaching intermediate levels. ILI and SARI cases have continued to decline over the last four EWs, with a higher proportion of ILI and SARI cases associated with influenza. By countries In Belize, influenza activity has risen in the last four EWs, reaching moderate levels. In the Dominican Republic, both RSV and influenza activities have maintained a decreasing trend over the last four EWs. In Haiti, SARI activity has fluctuated over the last four EWs, with a decrease in influenza and SARS-CoV-2 activity, remaining above the epidemic threshold in the last two EWs. In Jamaica, an increase in SARS-CoV-2 and RSV activity has been observed in the last four EWs, with moderate pneumonia levels and a slight decrease in the last EW. Santa Lucia has shown an increase in influenza activity in the last three EWs, 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 shown a slight increase in the last EW, and SARS-CoV-2 activity continues at low levels but has shown an increase in the last three EWs. Guyana has observed moderate levels of influenza activity in the last three EWs. The Cayman Islands have reported high influenza activity in the last four EWs and a slight increase in SARS-CoV-2 activity. Central America Influenza activity has decreased in the last EW, reaching low levels. Over the last four EWs, the predominant viruses have been B/Victoria, followed by A(H1N1)pdm09, and, to a lesser extent, A(H3N2). RSV activity has remained at moderate to high levels over the last four EWs. Although SARS-CoV-2 activity remains at low levels, there has been an increase in the last four EWs. ILI cases have shown an increase in the last four weeks, with the majority of positive cases attributable to SARS-CoV-2. SARI cases have remained on the decline over the last four EWs, with a higher proportion of cases associated with SARS-CoV-2 followed by influenza. By countries In El Salvador, RSV activity has decreased to low levels in the last four EWs, SARS-CoV-2 activity has shown a slight increase, and influenza activity has risen above the epidemic threshold. In Guatemala, RSV activity has decreased over the last four EWs to low levels, along with a decline in SARI cases, mostly positive for RSV. There has also been a slight increase in influenza activity, surpassing the epidemic threshold, coinciding with moderate ILI activity levels. In Honduras, RSV activity has shown a decrease 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 cases for influenza have increased in the last four EWs. In Nicaragua, influenza activity has remained fluctuating around epidemic levels in the last four EWs, and RSV activity has remained fluctuating at elevated levels. In Panama, RSV activity continues at elevated levels, albeit decreasing, while ILI and SARI cases have shown an increase in the last four EWs, with the majority of positive cases attributable to SARS-CoV-2. Andean Region Influenza activity, although remaining at low levels, has shown a slight increase in the last four EWs. During this period, the predominant influenza viruses have been A(H1N1)pdm09, with lesser circulation of B/Victoria. RSV activity has remained at low levels, with a slight increase over the last four EWs. SARS-CoV-2 activity has been on the rise over the last four EWs, reaching moderate to high levels. ILI and SARI activity in the subregion remain at low levels, with positive cases associated with influenza in most ILI cases and with influenza and RSV in SARI cases. By countries In Bolivia, the circulation of SARS-CoV-2 has remained high, and SARI cases have remained at epidemic levels over the last four EWs. In Colombia, SARS-CoV-2, RSV, and influenza activities have remained at low levels, with an increase in the last three EWs. SARI cases, in turn, have fluctuated 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 levels in the last four EWs, accompanied by an increase in SARI cases, at moderate levels, with the majority being positive for influenza. In Venezuela, influenza activity has remained fluctuating around the epidemic threshold over the last four EWs, with a slight increase in RSV activity. Brazil and the Southern Cone Influenza activity has remained at low circulation levels over the last four EWs. During this period, the predominant influenza viruses have been A(H3N2) and 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 over the last four EWs. SARI and ILI activity have remained low over the last four EWs, with the majority of positive cases attributable to SARS-CoV-2. By countries 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 has remained at high levels over the last four EWs. In Chile, very high SARS-CoV-2 activity has been maintained, with an increase in influenza activity above the epidemic threshold in the last four EWs. ILI cases are at epidemic levels, and SARI cases are below this threshold. In Paraguay, the circulation of SARS-CoV-2 has risen in the last four EWs to intermediate to high levels, with SARI activity decreasing to epidemic levels, and the majority of positive cases for ILI and SARI attributable to SARS-CoV-2. In Uruguay, SARI activity has remained on the decline in the last four EWs, with levels below the epidemic threshold, with the majority of positive cases attributable to SARS-CoV-2.