After falling slightly around the winter holidays, influenza activity has now risen for 2 consecutive weeks, according to a January 31 report from the US Centers for Disease Control and Prevention (CDC).
At a time when many are rightly concerned about the novel coronavirus (2019nCoV) — of which there are 11 confirmed cases in the United States as of Monday — the CDC is also warning citizens not to drop their guard about influenza, which has caused at least 19 million illnesses, 180,000 hospitalizations, and 10,000 deaths so far this season.
Nationwide, during the week ending January 25 (week 4), 5.7% of outpatient visits for influenza-like illness activity were reported, up from 5.1% the week before and above the national baseline of 2.4%. Regionally, this percentage ranged from 4.1% to 7.7% and visits were above region-specific baselines in all regions.
Activity was high in the District of Columbia, New York City, Puerto Rico, and 41 states — an increase from 35 the week before. Activity was moderate in seven states. There were insufficient data to calculate activity from the US Virgin Islands and two states (Delaware and Idaho).
Geographically, influenza activity was widespread in Puerto Rico and 49 states, regional in Hawaii, local in the District of Columbia, and sporadic in the US Virgin Islands. Guam did not report on activity.
Between Oct. 1, 2019 and Jan. 25, 2020, 8633 laboratory-confirmed influenza-associated hospitalizations were reported. Of those, 5173 (59.9%) were linked to influenza A virus, 3401 (39.4%) to influenza B virus, 27 (0.3%) to influenza A and influenza B virus co-infection, and 32 (0.4%) to influenza virus for which type was undetermined.
Among viruses for which influenza A virus subtype was available, 1080 (91.1%) were A(H1N1)pdm09 virus and 106 (8.9%) were A(H3N2).
Overall, the cumulative hospitalization rate was 29.7 per 100,000 population, "similar to what has been seen during recent previous influenza seasons at this time of year," the CDC says in the report. However, the CDC says rates in children and young adults are higher than those seen at this time during recent seasons.
The highest hospitalization rate is among adults aged 65 years and older (71.3 per 100,000 population), followed by children younger than 5 years (48.8) and adults aged 50 to 64 years (36.7).
The percentage of deaths that resulted from pneumonia and influenza was 6.7% — below the epidemic threshold of 7.2% for week 3.
During week 4, CDC received reports of 14 influenza-associated pediatric deaths that occurred between the weeks ending Nov. 9, 2019 and Jan. 25, 2020. Eight were linked to influenza B viruses, one of which underwent lineage determination and was a B/Victoria virus. Six were related to influenza A viruses; three of those were subtyped and found to be A(H1N1)pdm09 viruses.
There have been 68 influenza-related pediatric deaths so far during the 2019-2020 influenza season. Of those, 45 were linked to influenza B viruses; all eight that had lineage determined were B/Victoria viruses. Approximately one third (23) were related to influenza A viruses, of which 13 were subtyped and found to be A(H1N1)pdm09 viruses.
The vast majority (91.5%) of the 1108 hospitalized adults who had information on underlying conditions had one or more underlying medical conditions. The most common of these were cardiovascular disease, metabolic disorder, obesity, and chronic lung disease.
Among hospitalized children with information on underlying conditions, about half (46.5%) had one or more underlying conditions, the most common of which was asthma. Approximately one fourth (26.4%) of hospitalized women of childbearing age with pregnancy status recorded were pregnant.
Estimates of influenza vaccine effectiveness are not yet available for this season; however, the CDC emphasizes that vaccination is the best way to prevent influenza and its complications.
"Antiviral medications are an important adjunct to flu vaccine in the control of influenza. Almost all (>99%) of the influenza viruses tested this season are susceptible to the four FDA-approved influenza antiviral medications recommended for use in the US this season," the CDC writes in the report.
CDC FluView. Published online January 31, 2020. Full text
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