Public health officials are scrambling this week to isolate a measles outbreak at a day care center in Philadelphia.

Cases first appeared at Children’s Hospital of Philadelphia in early December. Health officials received notice days later that there were subsequent cases at a day care center in Northeast Philadelphia. On Monday, the city's public health department identified two new cases, bringing the number of people infected with the deadly and preventable virus to eight. At least five of the eight cases have resulted in hospitalization.

“We’re at a stage where we’re holding our breath,” Dr. Cheryl Bettigole, the health commissioner for the city of Philadelphia, told USA TODAY.

There is a highly effective vaccine against measles that has been around for decades. The disease typically spreads through coughing or sneezing.

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It took two weeks for the city to learn of the exposures at the day care facility, Bettigole said. Once word of the outbreak came, it was too late for children and adults at the facility to get a measles vaccine, if they didn't already have one. The vaccine can be administered to children as young as 6 months old in outbreak situations, Bettigole explained. Health officials have begun administering free vaccines at clinics.

“We're doing everything we can to make sure people have the information they need to keep others safe, to keep themselves safe,” Bettigole said.

First patient, infant, begins with travel abroad

The first case was an infant admitted as a patient at Children’s Hospital of Philadelphia between Dec. 6 and Dec. 9, with an infection that later presented as measles, according to the Philadelphia Inquirer. The infected infant traveled internationally, though it's unclear what country or region the child's family visited. The family came home to the Philadelphia area, and doctors at Children's Hospital treated the child for fever and respiratory symptoms.

It turned out to be measles. The infant infected three patients in adjacent rooms, setting off the outbreak, Bettigole said. The three patients were not immunized. Health officials noted that not everybody can be vaccinated, and age is a factor. Doses of the measles, mumps and rubella (MMR) vaccine begin at 12 to 15 months followed by a second dose when a child is between 4 and 6, according to the U.S. Centers for Disease Control and Prevention.

There were no other exposures at Children’s Hospital. People who were possibly exposed received post-exposure prophylaxis immune globin, using plasma containing antibodies to immediately protect against measles.

Just before Christmas, more cases were reported around the city. On Dec. 19, a patient infected at Children’s Hospital visited the Jefferson Health building, which has several clinics. There's no indication others became infected at that site.

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On Dec. 20, the same person attended the Multicultural Education Station, a day care center in Northeast Philadelphia, and exposed children and staff that day and Dec. 21. Two children at that facility tested positive. Last Friday, health officials identified three possible cases among children at the Multicultural Education day care facility.

By then, parents with sick children had visited several health facilities in Philadelphia and surrounding suburbs before the city health department received notice of their infections, putting additional institutions on notice for possible exposures to the virus. Officials are now looking for possible infections in the area of the day care center and other parts of the city with low vaccination rates, Bettigole said.

Several possible exposures identified

The city listed exposures at several health systems, noting dates that parents came with infected children to the sites for treatment and citing dates in case anyone was at these facilities at the relevant times:

• Children’s Hospital of Philadelphia’s emergency room on Dec. 28 and New Year’s Day; 
• Nemours Children’s Hospital, in Center City, on Dec. 29; 
• Christopher’s Hospital for Children, in North Philadelphia, in the emergency department on Dec. 30-31 and its inpatient unit between Dec. 31 and Jan. 3;
• Nazareth Hospital’s emergency department, in the city’s northeast, on Dec. 31 and Jan. 2;
• Jefferson Abington Hospital’s emergency room and Holy Redeemer Pediatric Urgent Care, both in suburbs just north of Philadelphia, on Jan. 3.

How does it spread?

The virus is extremely infectious, said Dr. Paul Offit, the director of the vaccine education center at Children's Hospital of Philadelphia and a professor of pediatrics at the University of Pennsylvania's Perelman School of Medicine. A person with the flu can infect about two or three people in a normal day, he explained, but a person with measles can infect about 18 people.

That’s because it’s spread by tiny aerosolized droplets that can infect someone simply by being in similar airspaces. They do not necessarily have to have direct contact. After an infected patient visits a room, it typically takes two hours before it's safe for people to enter the room, Offit said.

Symptoms typically present early on as high fever, cough, runny nose or red, watery eyes or pinkeye, the city health department said. A few days later, the person develops a higher fever presenting when a reddish or hyper-pigmented rash starts, first at the hairline on the face before spreading downward, to the neck, trunk, arms and legs; people can also develop tiny white spots, called Koplik spots, in the mouth.

Serious risks include death

About a fifth of people who get measles will be hospitalized, while one in 1,000 develop encephalitis, or swelling of the brain, which can result in convulsions, deafness or intellectual disabilities, the city health department said.

Deaths are commonly caused by pneumonia and dehydration. Nearly one to three in a thousand children with measles will die from respiratory or neurologic complications.

Measles was commonplace before the vaccine was developed in the early 1960s. Following national measles outbreaks in the 1980s and 1990s, officials began mandating two-dose vaccines that proved extremely effective, said Offit, of Children's Hospital. Philadelphia’s measles outbreak in the early 1990s resulted in multiple deaths and over 900 cases, stemming from two churches that didn't permit vaccinations.

About 93% of Philadelphia children are now vaccinated against measles by 6, according to the health department. Vaccination against the virus provides near total protection, but rates have declined nationwide due to misinformation around vaccines, including debunked conspiracies spread by presidential candidate Robert F. Kennedy Jr.

Declines in vaccination rates have brought about more cases, including an outbreak in Columbus, Ohio, in 2022 that infected 85 children. There have also been cases in the Chicago area and nearby Wisconsin this past fall.

“The measles vaccine is a victim of its own success,” said Offit, who authored “Vaccinated” about Dr. Maurice Hilleman, who helped develop several vaccines including for MMR. “It’s not just that we’ve largely eliminated measles from a time when we would have 3 to 4 million cases a year in this country. We’ve eliminated the memory. We don’t remember how sick it makes you.”

Bettigole, the health commissioner, said the number of different hospital visits in recent days of parents bringing their children infected with measles speaks to how severe their infections are. 

“The child is so sick that they keep coming back,” she said. “I think it’s a reminder to all of us (that) measles is a really serious infection. Fortunately, we have a great vaccine.”

The city health department is offering MMR vaccines, administered together, for free at its health centers, including with walk-ins available to Philadelphia residents.