Philadelphia measles outbreak ends, after starting at CHOP and spreading through day care

A measles outbreak that grew to nine cases in Philadelphia over six weeks is over, city health authorities said Tuesday.

The outbreak began in Children’s Hospital of Philadelphia in early December and spread to a day-care center in Northeast Philadelphia. Infections were confirmed in seven children and two adults.

Six people were hospitalized. All improved and ultimately went home, the Philadelphia Department of Public Health said.

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Measles is highly infectious and spreads through breathing in an airborne virus or touching contaminated surfaces, according to the U.S. Centers for Disease Control and Prevention. By some measures, measles is seven times more contagious than COVID-19. The virus can remain in the air for two hours.

The measles virus has an incubation period that can last up to 21 days. Health authorities declare measles outbreaks over after two incubation periods — or 42 days — pass without new infections. The last case in Philadelphia was identified on Jan. 16.

Even one dose of the MMR vaccine, which babies can receive when they are 1 year old, is 93% effective at preventing measles, according to the CDC. Two doses bring up that rate to 97%. People who were born before 1957, or have had measles, are also considered immune.

Landrus Burress, health department’s director of disease control, said in a statement that the outbreak remained contained because of the city’s 93% vaccination rate against measles, coupled with the collaborative efforts of authorities and health systems to identify cases and minimize exposure.

Prior outbreaks in Philadelphia were larger, such as in 1991 when 1,400 people were infected and nine children died.

“We were able to keep this outbreak small and quickly resolved,” Burress said.

The Philadelphia outbreak began with the hospitalization of an infant at CHOP who was recently in a country where the virus is more common. It took two days before the infant developed the rash characteristic to measles, and by that time, other patients were infected. They included an infant who was too young to get vaccinated, an unvaccinated older child, and the older child’s unvaccinated parent.

Before Christmas, one of the children who was exposed to measles violated quarantine guidelines and attended the Multicultural Education Station Day Care at 6919 Castor Ave. Four other children at that day-care center, and one parent, were subsequently diagnosed with the disease.

Outside of Philadelphia, authorities in Wilmington, Del., and Pennsylvania’s Delaware and Montgomery Counties have warned local residents of potential measles exposures from city residents who visited regional health-care facilities.

A child in Camden County tested positive for measles mid-January, but authorities did not say the case was related to the Philadelphia outbreak.

Other measles cases have been reported throughout the nation, including six cases in an ongoing Florida outbreak connected to an elementary school near Fort Lauderdale.

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The decline in routine childhood vaccination and the increase in anti-vaccination sentiment makes more outbreaks likely, Paul Offit, the director of the Vaccine Education Center at CHOP, told The Inquirer last month. The relatively small outbreaks like the one Philadelphia experienced this winter could be a warning of larger ones to come.

“It’s like the beginning of horror films, at some point one of the actors will say ‘did you hear something?’ and soon thereafter the monster appears,” Offit said. “That’s where we are.”