In the historical debate about whether healthcare workers should be required to have seasonal influenza shots, sometimes the issue of whether and how much flu is actually transmitted by caregivers has been viewed with some skepticism.
For example, an oft-cited 2013 Cochrane review concluded that there were “no accurate data” supporting the vaccination of healthcare workers to prevent laboratory-confirmed influenza in long-term care residents age 60 years and older.1
The point may have become somewhat moot as more hospitals mandate flu vaccination, but there is accumulating evidence that healthcare workers do transmit flu to patients, some of whom are in ICUs and may end up dying. That’s something of a broad take-away from a study2 presented recently in New Orleans at IDWeek 2016, as investigators with the CDC reported that 1% of flu cases reviewed were acquired in the hospital.
“Hospital-acquired influenza cases continue to occur and are likely underestimated,” said Charisse Cummings, MPH, an epidemiologist at the CDC who presented the study. “Clinicians should think to test patients for influenza in patients admitted for non-respiratory issues, who then develop respiratory illness during hospitalization.”
That percentage should be considered an undercount because the study design ruled out many cases for insufficient data, erring on the side of a conservative case count that was also limited by whether or not a provider decided to order a flu test on a given patient. Vaccination rates of healthcare workers or possible factors contributing to transmission were not assessed as part of the study.
“Hospital acquired (HA) influenza represented 1% of patients in our hospital surveillance over four influenza seasons,” the researchers reported. “Since testing was clinician-driven, prevalence may have been under-detected if influenza was not suspected and tested. Influenza vaccination in healthcare workers and family members of high-risk persons, good hospital infection control [to prevent transmission from other patients], and limiting ill persons from visiting or working in hospitals should be encouraged.”
The study included patients from the CDC’s Influenza Hospitalization Surveillance Network from 2011 to 2015. The flu had to be confirmed by symptoms and testing more than three days after admission to be considered hospital acquired.
Overall, 41,974 patients had flu and the researchers determined that 463 (1%) of them acquired it in the hospital. Those hospital acquired cases included 417 adults and 46 children. Of interest regarding discussions of the healthcare continuum, 31 (7%) of the cases determined to be hospital acquired had been transferred from another hospital and 66 (14%) came in from a nursing home, the researchers reported.
Overall, 91% of those who acquired flu in the hospital had underlying medical conditions, principally cardiovascular, neurologic, immunological, and renal problems.
“The median length of stay after influenza diagnosis was 6 days.” the researchers reported. “Of 463 HA cases, 126 (27%) were in the intensive care unit before HA influenza diagnosis, 22 (5%) were admitted to the ICU on or after the date of HA influenza diagnosis and 36 (8%) died.”
“Among cases with complete ICU admission and discharge dates 30% developed hospital acquired influenza during ICU stay,” Cummings said. “In addition, [another] 30% who tested positive one to seven days after ICU discharge, may have been exposed to influenza during their ICU stay. The length of stay was considerably longer for hospital-acquired influenza compared to community acquired influenza.”
REFERENCES
- Thomas RE, Jefferson T, Lasserson TJ. Influenza vaccination for healthcare workers who care for people aged 60 or older living in long-term care institutions. Cochrane Database Syst Rev 2013;7(7):CD005187 pmid:23881655.xa
- Cummings CN, Garg S, Nenninger EK, et al. Hospital-Acquired Influenza Among Hospitalized Patients, 2011–2015. Oral abstract session. IDWeek Oct. 26-30, 2016. New Orleans, LA.
