Overall hospitalizations for influenza-like illness (ILI) are at their highest since the US Centers for Disease Control and Prevention (CDC) began collecting such data, according to new information presented during a teleconference by the CDC today.

“In the past week, we have seen increased [ILI] activity, more hospitalizations, and tragically, more flu-associated deaths in children and adults,” Anne Schuchat, MD, RADM, USPHS, and acting director, CDC, said. “As of this week, overall hospitalizations are now the highest we’ve seen, even higher than in 2014-2015, our previous high season.”

Reports of crowded hospitals and spot shortages of antiviral drugs and rapid influenza tests continue. “Unfortunately, our latest tracking data indicate that flu activity is still high and widespread across most of the nation,” Dr Schuchat added.

Unusual Pattern

“”[T]his season is turning out to be a particularly challenging one, and it has been compounded by lots of flu occurring nationwide simultaneously over several weeks,” said Dan Jernigan, MD, MPH, CAPT, USPHS, director, Influenza Division, National Center for Immunization and Respiratory Diseases. “This is an unusual pattern for flu in the [United States].”

For the 3 weeks prior to the current week, influenza activity was widespread in 49 states — something that has not occurred since the CDC began collecting influenza activity data. That number fell to 48 states this week, with Oregon and Hawaii reporting decreased activity.

The percentage of patients seen in physicians’ offices, urgent care clinics, and emergency departments for ILI increased again this week, going from 6.6% last week to 7.1% this week. For two seasons during the past 16 years rates, have been higher than that — the 2009 H1N1 pandemic peaked at 7.7%, and the 2003-2004 season, which was a high-severity H3N2 season, peaked at 7.6%, Dr Jernigan explained.

The level of ILI activity has been elevated for 10 consecutive weeks. During the past five seasons, the average duration of an influenza season has been 16 weeks, ranging from 11 to 20 weeks. “There may be many weeks left for this season to go,” Dr Jernigan said.

The number of states that reported high ILI activity this week rose from 39 to 42. In the western states, activity is starting to decrease, the eastern part of the country is seeing higher activity, and southern states continue to report high activity, with levels similar to those of previous weeks.

“For the second week in a row, there are signs that activity in the West may be easing up. However, we are by no means out of the woods. Most seasons last up to 20 weeks, and we’ve probably got several weeks left of increased flu activity,” Dr Schuchat explained.

High-Severity Season

The CDC collects information about laboratory-confirmed influenza hospitalizations in 13 states, which represent a population of approximately 9% of the United States. During the past few weeks, hospitalizations have tracked closely with the 2014-2015 season, which was described as representing high severity, with an estimated 710,000 hospitalizations during the season.

The CDC reports that for this week, the cumulative hospitalization rate was 51.4 per 100,000, which is higher than the 43.5 per 100,000 reported at this same week during the 2014-2015 season. If that trend continues through the season, the number of influenza hospitalizations may exceed 710,000. The highest hospitalization rates are among those aged 65 years and older, followed by individuals aged 50 to 64 years and children younger than 5 years.

Hospitalization rates continue to be significantly higher in some states. Although rates were lower during the past week, cumulative hospitalization rates in California were approximately four times higher than during 2014-2015, and rates were double for that period in Oregon and Minnesota.

In adults, the number of deaths from pneumonia and influenza also increased during the past week, from 9.1% to 9.7%. “This is not as high as during seasons 2012-2013 and 2014-2015, where they peaked at 11.1% and 10.8%, but it is possible that this season will reach or surpass those two severe seasons,” Dr Jernigan said.

Most (76%) of the 45,000 respiratory specimens tested in state public health laboratories this season are influenza A (H3N2), although influenza A (H1N1) and influenza B viruses are also circulating.

Among H3N2 viruses evaluated by the CDC and five other World Health Organization–designated laboratories, there is no evidence that the virus has significantly drifted; however, viruses that have been prepared for use in vaccines “have adaptations that make them less similar to the circulating H3N2 viruses,” Dr Jernigan explained.

Children Particularly Hard-hit

Pediatric deaths from influenza are the highest since 2014-2015. An additional 16 influenza-related pediatric deaths were reported this week, totaling 53 children this season.

Of the children who died from influenza, only about 20% were vaccinated, and half were otherwise healthy.

Hospitalizations among children are tracking lower than during the 2014-2015 season, although it is too soon to know how many such hospitalizations will occur by the end of the season.

Dr Schuchat urged parents of children to call their primary care provider or a nurse hotline before taking their child to the doctor or emergency department. “In general, worrisome signs are very high, persisting fever, difficulty breathing or shortness of breath, rapid heartbeat or shallow, rapid breathing, or significant tiredness or confusion. In very young children, those kinds of symptoms are going to be difficult to assess, and so we really do think that a call to the pediatrician or nurse hotline is very important,” she explained.

When seeking medical care at the clinic or hospital, parents should cover the child’s mouth with a mask if the child is coughing.

A red flag for children and adults alike is an individual’s showing signs of improvement, and then suddenly becoming worse. That can indicate the development of a secondary bacterial pneumonia, which could be a “bad emergency,” Dr Schuchat said.

Concerns About Flu Shot Effectiveness This Year

There are ongoing concerns about the vaccine’s effectiveness.

Dr Schuchat said the CDC is concerned that the current vaccine’s effectiveness against H3N2 viruses “is lower than against other types and that in recent years, it’s been more challenging to even get effective H3N2 protection,” she explained.

She said the CDC recommends the influenza vaccine, “even though we know that most vaccines have low effectiveness against H3N2 viruses.” Effectiveness is better against other influenza viruses, and there is more than one circulating influenza virus. The vaccine may also reduce the severity of symptoms in those who develop influenza. It is not too late to get vaccinated, she added.

Bacterial pneumonia can be a serious complication of influenza, and viral infections such as influenza can make individuals more susceptible to secondary bacterial infections. Individuals who appear to be getting better and suddenly worsen should seek medical attention.

Pneumococcal pneumonia is a common culprit in secondary bacterial pneumonias, and the CDC recommends vaccination against pneumococcal pneumonia for those aged 65 years and older.