Virginia health officials have found that the number of reported outbreaks of respiratory illnesses this summer, such as one that contributed to the deaths of three people and sickened dozens more at an assisted-living facility in Northern Virginia, has increased by roughly half.

Jonathan Falk, epidemiology program manager at the Virginia Department of Health, said the number of such outbreaks this year rose to 19, compared with the dozen or so that normally occur in the period outside flu season. Several infections occurred in assisted-living or other long-term care settings for older people, such as an outbreak at Greenspring Village in Springfield.

Three people died, 23 were hospitalized and dozens more fell ill during an outbreak of respiratory illnesses that struck Garden Ridge, the community’s assisted-living and skilled nursing unit, between June 30 and July 15. The infection also spread to Greenspring’s staff, affecting 19 employees at the complex, Fairfax County health officials said.

It’s not clear why the outbreak occurred at Greenspring or why there has been an increase in reported cases around Virginia, health officials said. Neither the District nor Maryland has detected anything similar, according to state health department officials in those jurisdictions.

The increase in respiratory infections in Virginia prompted M. Norman Oliver, the commonwealth’s health commissioner, to issue an advisory last month to clinicians, alerting them to the increase, particularly in settings for long-term care. The July 19 advisory urged medical personnel and residential managers to take precautions, especially because of an imminent heat wave at the time.

“We were well above a dozen outbreaks reported in our system,” Falk said. “And that’s not even getting into the back-to-school season.”

In the period since mid May, when flu season winds down, and October, when the number of cases picks up again, Virginia’s statewide reporting system has counted 19 outbreaks, including 13 at long-term care facilities. That compares with 13 similar outbreaks outside of flu season in 2018 and 15 in the previous year, Falk said. He said he did not have immediate figures on how many people were hospitalized as a result.

Virginia health officials noted that laboratory tests identified a variety of causes of the outbreaks, including pathogens for Legionnaire’s disease, flu, the common cold and pertussis, or whooping cough. In some cases, no common agent has been identified. In an update on July 29, the Fairfax County Health Department said testing conducted by the federal Centers for Disease Control and Prevention on samples from Greenspring identified the virus that causes the common cold. There have not been an unusual number of illnesses reported there since July 15, officials said.