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ATLANTA – If your ED waiting room seemed to be a little less packed this winter, here’s a possible explanation: The 2015–16 influenza season was less severe than the previous three seasons.
The CDC urges healthcare providers to remain vigilant about identifying influenza viruses throughout the summer, however, even though the season traditionally has lower rates of illness.
In a report in the Morbidity & Mortality Weekly Report, the CDC also reports that the season peaked in mid-March, somewhat later than usual. Public health officials note that influenza A(H1N1)pdm09 viruses predominated overall, but influenza A(H3N2) and influenza B viruses also circulated.
“The season was less severe overall compared with the preceding three seasons, including 2013–14, the last influenza season when influenza A(H1N1)pdm09 was the predominant virus,” according to the MMWR article. “Whereas influenza A(H3N2)–predominant seasons are typically more severe overall than influenza A(H1N1)pdm09–predominant seasons, and are especially severe among the elderly and the very young, influenza A(H1N1)pdm09 viruses have been associated with severe illness in younger adults since the virus emerged during the 2009 pandemic, when mortality rates were highest in adults aged 50–64 years, and again during the 2013–14 season, when adults aged <65 years were at high risk for severe influenza illness.”
Cumulative hospitalization rates for adults aged 50–64 years were 45.2 per 100,000 population this season and 53.7 per 100,000 population in the 2013-14 season, according to the CDC, which points out that “although some age groups are at high risk for developing influenza-related complications every year, influenza can cause severe illness in persons of any age, including adults aged 50–64 years.”
The report urges emergency physicians and others to continue testing for seasonal influenza viruses and monitoring for novel influenza A virus infections throughout the summer.
“Although summer influenza activity in the United States typically is low, influenza cases and outbreaks have occurred during summer months, and clinicians should remain vigilant in considering influenza in the differential diagnosis of summer respiratory illnesses,” according to the overview report. “Healthcare providers also are reminded to consider novel influenza virus infections in persons with [influenza-like illness], with swine or poultry exposure, or with severe acute respiratory infection after travel to areas where avian influenza viruses have been detected, especially if there was recent close contact with animals such as wild birds, poultry, or pigs.”
Local and state public health departments should be alerted if a human infection with a novel influenza virus infection is suspected, the CDC emphasized.
Public health officials also continued the push for rapid use of antiviral medications to lessen the severity and duration of influenza, underscoring that patients with confirmed or suspected disease who have severe illness, require hospitalization, or are at high risk for influenza-related complications should be treated with antivirals as soon as possible. They emphasized that, in those patients, treatment with antivirals should not be delayed while awaiting confirmatory influenza test results “because early treatment is most effective and rapid antigen detection influenza diagnostic tests can be insensitive.”