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Influenza activity has decreased slightly, but "remains relatively high for this time of year," according to the Center for Disease Control and Prevention (CDC).
Influenza activity was at or above baseline levels for 18 weeks in the United States, compared to 16 weeks for the past five seasons, the CDC reported in a March 29 report for the week ending March 23 (week 12).
Influenza seasons have ranged from 11 to 20 weeks over the past five seasons and CDCs expect to see high influenza activity for several weeks.
Most of the northern hemisphere is also experiencing a decline in influenza levels, the World Health Organization announced on April 1.
Earlier in the season, influenza A (H1N1) pdm09 – which generally causes a less severe disease – was the predominant strain in the United States; However, H3N2 viruses have been predominant since the end of February.
Influenza B viruses have been reported in small numbers.
"A (H3) viruses are generally badociated with a more serious disease in the elderly, and the influenza vaccine may be less protective against A (H3) disease than other components of the virus, making treatment particularly important. Influenza antiviral early in this age group, during the current period of predominance A (H3), "said the CDC in a summary of the report.
Health Notice
On March 28, the CDC issued a health advisory inviting clinicians to remain vigilant against influenza and recommending rapid antiviral treatment if there is suspicion of influenza in high-risk patients.
The proportion of outpatient clinic visits for ILI has fallen from 4.3% to 3.8% and continues to exceed the national baseline of 2.2%. Influenza activity peaked at 5.1% in the week ending February 16 (week 7) and ranged from 3.6% in 2015-16 to 7.5% in 2017-18.
In the United States, all regions experienced influenza-like illness at or below their baseline.
Influenza-like illness activity was high in 20 states; moderate in Puerto Rico and 13 states; low in New York City, the District of Columbia and seven states; and minimal in 10 states. The US Virgin Islands did not have enough data to report.
Influenza was widespread geographically in Puerto Rico and in 34 states, regional in 14 states, local in two states, and sporadic in the US Virgin Islands. Guam has not reported any influenza activity.
The cumulative rate of laboratory-confirmed influenza-badociated hospitalizations was 52.5 per 100,000 population, up 47.1 from the previous week. The highest hospitalization rate was observed among adults aged 65 and over (167.0 per 100,000 population). The hospitalization rate was 67.4 per 100,000 population for adults aged 50 to 64 and 63.6 per 100,000 for children under 5 years of age.
The proportion of deaths badociated with pneumonia and influenza exceeded the epidemic threshold of the mortality surveillance system of the National Center for Health Statistics.
A pediatric death badociated with influenza was reported during the week ending March 23, for a total of 77 this season.
Most influenza viruses characterized antigenically are similar to the reference viruses developed on cells that correspond to those used in vaccines for the northern hemisphere 2018 – 2019. "However, a growing proportion of influenza A (H3N2) viruses is distinguished antigenically from A / Singapore / INFIMH-16-0019 / 2016 (3C.2a1), a cell-propagating reference virus representing component A (H3N2) of 2018-19 influenza vaccines from the Northern Hemisphere ", explains the CDC in his summary report.
Almost all (> 99%) of the influenza viruses tested were sensitive to oseltamivir and peramivir and all were sensitive to zanamivir.
In the temperate regions of the southern hemisphere, influenza activity has been maintained at off-season levels, with the exception of parts of Australia where it has remained above the inter-season levels.
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