Regional Update, Influenza and Other Respiratory Viruses. Epidemiological Week 37 (20 September 2024)

[WEEKLY SUMMARY]. Regional Situation: Influenza-Like Illness (ILI) and Severe Acute Respiratory Infection (SARI) activity have shown an overall decreasing trend in recent epidemiological weeks (EWs). In North America and the Caribbean, most cases have been associated with SARS-CoV-2 and, to a lesser extent, influenza, both of which are declining. In Central America, the Andean region, and the Southern Cone, cases have decreased, with most positive results linked to RSV, SARS-CoV-2, and influenza. SARS-CoV-2 activity remains elevated in North America, though it has begun to decrease in most countries, as well as in some areas of the Caribbean and the Andean subregion, where the declining trend continues. In contrast, a slight increase has been observed in Brazil and the Southern Cone. Influenza has shown a general decline, although it continues to fluctuate in certain Caribbean and Andean countries. Meanwhile, RSV activity has started to decline in the Andean subregion and the Southern Cone, following epidemic levels in previous weeks, but remains high in some Central American countries. North America: Cases of ILI, SARI, and hospitalizations associated with respiratory viruses, after showing an increase in previous weeks, have started to decrease. 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 previous 2023-2024 wave. By country: • In Canada, SARS-CoV-2 activity remains on the rise, 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 over the last four weeks to epidemic levels. 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 declined over the last four weeks. SARS-CoV-2 positivity levels, after reaching values similar to the peaks observed in 2023 and 2024, have shown a decreasing trend over the last four EW. Influenza and RSV activity continue to remain low. Caribbean: ILI cases have maintained a declining trend, associated with a higher proportion of positive influenza cases. SARI cases have remained low, with most positive cases associated with SARS-CoV-2. 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 compared to previous waves, although declining. By country: In the last four EW, influenza activity has been observed in Belize, the Dominican Republic, Saint Lucia, Suriname, and Guyana. Additionally, SARS-CoV-2 activity has been recorded in Haiti, Jamaica, Saint Lucia, Barbados, Guyana, and Saint Vincent and the Grenadines. RSV activity has also been detected in the Dominican Republic and Guyana. • In Jamaica, there has been an increase in SARI cases, which remain below the epidemic threshold, as well as pneumonia cases at moderate levels. This coincides with the peak in SARS-CoV-2 positivity detected in previous weeks, which is now declining. • In Guyana, after an increase in ILI and SARI activity in previous weeks, a decline has been observed in the most recent EW, with positive cases attributable to influenza, and to a lesser extent, SARS-CoV-2 and RSV. • In Saint Lucia, an increase in SARI activity has been detected, fluctuating around the epidemic threshold over the past four EW, coinciding with the circulation of SARS-CoV-2 and, to a lesser extent, influenza. Central America: A decline in ILI and SARI activity has been observed over the past four EW, with most positive ILI cases attributable to SARS-CoV-2, which is declining, and most positive SARI cases attributable to RSV, which is increasing. Influenza activity, after reaching epidemic levels in several countries of 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 remains on the 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 to low levels. By country: • In Costa Rica, following the increase in ILI and SARI cases in previous weeks, a decreasing trend has been observed over the past four EW to epidemic levels. Most positive ILI cases are attributable to SARS-CoV-2, and most positive SARI cases are attributable to RSV. SARSCoV- 2 activity, after reaching peak levels seen in previous waves, has declined. RSV activity has shown a slight increase, although it remains low compared to previous seasons. 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. RSV activity remains low. • In Guatemala, there has been a slight increase in ILI activity to epidemic levels, with most positive cases attributable to influenza, and to a lesser extent, SARS-CoV-2 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, both of which are declining to low levels. • In Nicaragua, influenza levels have been below the epidemic threshold over the last four EW, and SARS-CoV-2 circulation remains low. However, RSV positivity rates have risen to levels similar to the peaks observed in previous seasons and continue to rise. • In Panama, ILI and SARI cases, after the increase observed in previous weeks, have shown a slight decline over the past four EW. Most positive cases are attributable to RSV, whose activity, after a significant increase to levels similar to those observed in previous seasons, has begun to decline. Additionally, fewer positive cases of SARS-CoV-2 have been detected, with activity remaining low. 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 and declining, with the predominant viruses being B/Victoria, followed by A(H3N2). RSV activity has been decreasing at moderate levels, and 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 activity. • In Colombia, ILI and SARI activity have 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 declined to low levels. Acute Respiratory Infection (ARI) cases have decreased to epidemic levels. • In Ecuador, SARI and pneumonia activity have shown a decline, reaching levels around the epidemic threshold. Positive SARI cases are mainly attributed to influenza, whose activity is fluctuating at epidemic levels, and to a lesser extent, SARS-CoV-2, which, after increased activity in previous weeks, is now declining. • 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, whose activity is also decreasing. ILI activity, after showing an uptick associated with an increase in the proportion of positive SARS-CoV-2 cases, has now recorded a decline over the last two EW. Influenza activity remains below the epidemic threshold in most countries. During this period, the predominant influenza viruses have been B/Victoria, followed by A(H1N1)pdm09 and, to a lesser extent, A(H3N2). By country: • In Argentina, ILI activity, after reaching high levels, has declined to levels below the epidemic threshold. Meanwhile, SARI activity, after reaching epidemic levels, has also fallen below this threshold. Influenza activity remains at epidemic levels, showing a slight uptick over the last two EW. 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, influenza activity remains below the epidemic threshold, and RSV activity remains low. Additionally, SARS-CoV-2 activity has shown a slight increase, although it remains low compared to previous waves. • In Chile, after the uptick in ILI and SARI cases, a decline has been recorded to moderate and epidemic levels, respectively. Most positive SARI cases are attributable to RSV, whose activity remains elevated, although with positivity levels below the peaks observed in previous seasons. Positive ILI cases are attributable to both RSV and influenza, whose activity, while remaining below the epidemic threshold, has shown a slight increase in recent weeks. SARS-CoV-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, RSV, and influenza, but remains below the epidemic threshold. Influenza activity has shown a slight uptick over the last two EW, reaching levels around the epidemic threshold. • In Uruguay, ILI and SARI activity have shown a progressive decline to epidemic levels, with most positive cases attributable to RSV, whose positivity levels have exceeded the peaks observed in previous seasons and are now declining. Influenza and SARS-CoV-2 activity remain low.