Regional Update, Influenza and Other Respiratory Viruses. Epidemiological Week 35 (6 September 2024)

ABSTRACT

[WEEKLY SUMMARY]. Regional Situation During the last four epidemiological weeks (EW), there has been a decrease in Influenza-Like Illness (ILI) activity, with cases reported in the Southern Cone, the Caribbean, and Central America. Additionally, epidemic levels of Severe Acute Respiratory Infection (SARI) have been reported in the Southern Cone, the Andean subregion, and Central America, mainly associated with the circulation of RSV and SARS-CoV-2. Regarding the circulation of respiratory viruses at the regional level, elevated SARS-CoV-2 activity has been observed, particularly in North America, the Caribbean, and the Andean subregion, with a declining trend in the latter two regions. Although influenza activity has decreased, it remains fluctuating in some Caribbean countries and the Andean subregion. Meanwhile, RSV activity has reached epidemic levels in Central America, the Andean subregion, and the Southern Cone. North America Cases of ILI, SARI, and hospitalizations associated with respiratory viruses, after showing an increase in previous weeks, have begun to decline. The majority of positive cases are attributable to SARS-CoV-2, although this proportion is also decreasing. Influenza activity has remained below the epidemic threshold in all countries. During this period, the predominant influenza viruses have been A(H3N2), followed by A(H1N1)pdm09 and B/Victoria. RSV activity has remained low. In contrast, SARS-CoV-2 activity has remained at levels similar to the peaks observed in the 2023-2024 wave. By country • In Canada, SARS-CoV-2 activity has increased, reaching levels close to the peaks recorded in previous waves. Influenza activity remains below the epidemic threshold, while RSV activity remains low. • In Mexico, after rising to moderate levels in previous epidemiological weeks, ILI and SARI cases have shown a marked decline in the last four weeks. Most positive cases are attributable to SARS-CoV-2, which is currently declining. Both influenza and RSV activity remain low. • In the United States, the hospitalization rate associated with SARS-CoV-2 per 100,000 inhabitants has shown a decline over the last three weeks, and SARS-CoV-2 positivity rates have reached values similar to the peaks observed in 2023 and 2024. Influenza and RSV activity continue to remain low. Caribbean Following the rise observed in previous weeks, ILI cases have shown a declining trend over the past four EW, associated with a higher proportion of positive influenza cases. SARI cases have remained low, though with an increasing proportion of positive SARS-CoV-2 cases. Influenza activity has been declining over the past four EW, with A(H3N2) being predominant, followed by A(H1N1)pdm09. RSV activity has remained low, while SARS-CoV-2 activity remains high. By country In the last four EW, influenza activity has been observed in Belize, the Dominican Republic, and Guyana. Additionally, SARSCoV- 2 activity has been recorded in Belize, Haiti, Jamaica, Barbados, Guyana, and Saint Vincent and the Grenadines. • In Guyana, following an increase in ILI and SARI activity in previous weeks, a decline has been observed in the last two EW, with positive cases attributable to influenza, and to a lesser extent, SARS-CoV-2. Central America After the increase in ILI and SARI activity observed in previous weeks, there has been a decline over the past three EW, with most positive cases attributable to SARS-CoV-2, which is decreasing, and RSV, which is increasing. Influenza activity, after reaching epidemic levels in several countries in the subregion, has declined over the past four EW. During this period, the predominant influenza viruses have been B/Victoria, followed by A(H3N2). RSV activity continues to rise, reaching levels similar to the peaks recorded in previous seasons. After reaching levels similar to the peaks observed in previous waves, SARS-CoV-2 activity has shown a downward trend over the past four EW. By country • In Costa Rica, following the increase in ILI and SARI cases in previous weeks, a declining trend has been observed over the past four EW. Most positive ILI cases are attributable to SARS-CoV-2, while most positive SARI cases are attributable to RSV. SARS-CoV-2 activity, after reaching peak levels seen in previous waves, has declined. RSV activity has shown a slight increase, although it remains low. Influenza activity remains below the epidemic threshold. • In El Salvador, after reaching moderate levels, influenza circulation has shown a decline over the past four EW, falling below the epidemic threshold. After a slight increase, SARS-CoV-2 activity remains low compared to previous waves. • In Guatemala, there has been an increase in ILI activity to moderate levels, with most positive cases attributable to SARS-CoV-2, and to a lesser extent, influenza and RSV. SARI activity has also increased to epidemic levels, with a significant rise in the proportion of positive RSV cases. • In Honduras, over the past four EW, SARI activity has fluctuated at epidemic levels, mainly associated with positive influenza cases, which are currently fluctuating at epidemic levels, and to a lesser extent, SARS-CoV-2 and RSV. • In Nicaragua, after influenza circulation exceeded the elevated threshold, levels have fallen below the epidemic threshold over the past four EW, and SARS-CoV-2 circulation remains low. However, RSV positivity rates have risen to the peaks observed in previous seasons. • In Panama, ILI and SARI cases, after the increase observed in previous weeks, have experienced a slight decline over the past four EW. Most positive cases are attributable to RSV, whose activity has shown a significant increase, reaching levels similar to those observed in previous seasons. To a lesser extent, positive cases are attributable to SARS-CoV-2, whose activity remains low. Additionally, influenza activity has remained below the epidemic threshold. Andean ILI and SARI activity has shown a decline over the past four EW in most countries. Influenza activity has remained low, with the predominant viruses being B/Victoria, followed by A(H3N2). RSV activity has remained stable at moderate levels, while SARS-CoV-2 activity is declining after reaching moderate levels compared to previous waves. By country • In Bolivia, SARI cases are below the epidemic threshold. Influenza activity has decreased to levels below this threshold. SARS-CoV-2 and RSV activity remain low, with a slight increase in SARS-CoV-2. • In Colombia, ILI and SARI activity has declined below the epidemic threshold over the past four EW. Most positive cases are attributed to RSV, whose activity is declining, and to a lesser extent, SARS-CoV-2, which, after reaching circulation levels similar to the peaks observed in previous waves, has shown a decline. Acute Respiratory Infection (ARI) cases have decreased to epidemic levels. • In Ecuador, SARI and pneumonia activity has remained at epidemic levels over the past four EW. Positive SARI cases are mainly attributed to influenza, which is at epidemic levels, and to a lesser extent, RSV and SARS-CoV-2, which is increasing. • In Peru, after the increase in SARS-CoV-2 activity observed in previous weeks, a decline has been detected, with levels lower than in previous waves. RSV activity has decreased, and influenza activity remains below the epidemic threshold. • In Venezuela, a decline in influenza activity has been observed, and RSV activity remains low. Brazil and the Southern Cone Following the increase observed in previous weeks, SARI activity has shown a decline over the past four EW, with most positive cases attributable to RSV. ILI activity has shown an uptick, associated with an increase in the proportion of positive SARS-CoV-2 cases. Influenza activity is declining, remaining below the epidemic threshold in most countries. During this period, the predominant influenza viruses have been B/Victoria, followed by A(H1N1)pdm09 and A(H3N2). RSV activity has shown a decline after reaching levels below the peaks observed in previous seasons. SARS-CoV-2 activity continues to increase, although still at low levels compared to previous waves. By country • In Argentina, ILI activity, after reaching high levels, has declined to levels below the epidemic threshold, while SARI activity, after reaching epidemic levels, has also fallen below this threshold. Influenza activity, after reaching high levels, has declined to epidemic levels. Meanwhile, RSV, after reaching positivity levels similar to the peaks observed in previous seasons, has shown a declining trend, while SARS-CoV-2, although at low levels, has shown a slight increase. • In Brazil, ILI and SARI activity have declined to levels below the epidemic threshold. Influenza activity is also decreasing below the epidemic threshold, while RSV activity remains low. However, SARS-CoV-2 activity has shown a slight increase, although it remains low compared to previous waves. • In Chile, after the uptick observed in ILI and SARI cases, with extraordinary and epidemic levels, respectively, a slight decline has been observed. Most positive cases are attributable to RSV, whose activity remains elevated, although with positivity levels below the peaks observed in previous seasons. Influenza activity, after reaching extraordinary levels, has declined below the epidemic threshold. SARSCoV- 2 activity remains low. • In Paraguay, SARI activity remains at moderate levels, with most positive cases attributable to RSV, whose activity is declining, and to a lesser extent, SARS-CoV-2, whose activity is increasing. ILI activity has shown a slight uptick associated with SARS-CoV-2 and RSV but remains below the epidemic threshold. • In Uruguay, ILI and SARI activity have declined to epidemic levels, with most positive cases attributable to RSV, whose activity has reached positivity levels higher than the peaks observed in previous seasons.Influenza and SARS-CoV-2 activity have remained low.