US Flu Cases Increased by 4 Million Over the Last Week

New data from the US Centers for Disease Control and Prevention (CDC) indicate that influenza activity in the United States has increased over the last 2 weeks.

The most recent statistics, collected through the week ending January 25, 2020, report that there have been 19 million cases of influenza during US 2019-20 flu season. This is an increase of 4 million cases since the last report.

Additionally, the CDC has recorded 180,000 hospitalizations and 10,000 deaths from the flu thus far. Based on these figures, severity is not considered high at this point in the flu season.

Over the past week the percentage of deaths attributed to pneumonia rose to 6.7% but remains below the epidemic threshold of 7.2%. Additionally, the hospitalization rate rose from 24.1 per 100,000 to 29.7 per 100,000, which is considered to be consistent with this time of year from recent seasons.

However, FluView statistics indicate that hospitalization rates are higher in children and young adults than at this time in recent seasons. At this time the highest rate of hospitalizations have been recorded in adults aged >65 years, followed by children aged 0-4 years, and adults aged 50-64 years.

Of 1108 adults hospitalized for influenza with information available, 91.5% had at least 1 reported underlying medical condition, most commonly cardiovascular disease, metabolic disorder, obesity and chronic lung disease.

Among 216 hospitalized women between 15-44 years with information on pregnancy status, 26.4% were pregnant.

Additionally, of 271 hospitalized children with information available, 46.5% had at least 1 underlying medical condition, with asthma reported most commonly.

Over the last reporting week, 14 new pediatric influenza-associated deaths were recorded, bringing the seasonal total to 68. According to CDC, of these 14 deaths, 8 were associated with influenza B—1 of which was determined to be a B/Victoria virus— and 6 were associated with influenza A, all of which were found to be A(H1N1)pdm09 viruses.

Outpatient influenza-like illness and laboratory data remain elevated and increased again this week. The number of jurisdictions experiencing high influenza-like-illness activity increased from 37 last week to 44 this week. Additionally, the number of jurisdictions reporting regional or widespread influenza activity increased to 51 this week.

Nationally and in some US regions, the proportions of influenza A (H1N1)pdm09 are increasing compared with influenza B viruses.

Nationally, influenza B viruses are the most commonly reported influenza viruses among children age 0-4 years (58% of reported viruses) and young adults 5-24 years (72% of reported viruses). On the other hand, A(H1N1)pdm09 viruses are the most commonly reported influenza viruses among adults 25-64 years (50% of reported viruses) and those 65 and older (57% of reported viruses).

According to FluSight forecasting, as of January 27^th, forecasts indicate that flu activity is likely to remain elevated through the rest of the month of February.

The CDC notes that estimates on flu vaccine effectiveness are not available for the 2019-20 US flu season yet, but vaccination is always the best way to protect against the flu and associated complications.

Based on the current status of the flu season and the forecast for the rest of the month, the CDC is reminding Americans that antiviral treatments are effective when initiated soon after onset of illness.

Antivirals, when started within 2 days of becoming ill, can lessen fever and flu symptoms and reduce the duration of illness. Additionally, antivirals can reduce the risk of complications such as ear infections in children and reduce complications that require antibiotics and hospitalization in adults.