The battle to halt the spread of the measles outbreak that began at Disneyland has required both infectious disease expertise and a good amount of old-fashioned detective work.
Health officials in California and seven other states have painstakingly traced the steps of measles patients, tried to identify anyone who came in contact with them, and quarantined those at greatest risk of getting the highly contagious disease to keep the virus from spreading.
It's a trail that has taken them to grocery stores, gyms, farmers markets, hospitals, post offices, banks, schools, a casino and even Starbucks and Wal-Mart. Shoppers at Costco in Gilroy were greeted with a public notice stating: "If you were in this store on Sunday January 18, 2015 between 4:00-6:00 p.m., you may have been exposed to measles."
In Arizona, which is hosting the Super Bowl on Sunday, health officials have been busy compiling a list of 1,000 people who might have been exposed to measles based on the movements of seven infected patients. They are urging unvaccinated children and adults in that group to stay away from public places for 21 days.
"All it takes is a quick trip to the Costco before you're ill and, bam, you've just exposed a few hundred people," Arizona Department of Health Services Director Will Humble said. "We're at a real critical juncture."
Officials are using a tried-and-true playbook for tracing infectious diseases. But it's on a much grander scale than recent measles outbreaks because it started at a bustling international tourist destination and has spread across multiple states as well as Mexico. Officials at the U.S. Centers for Disease Control and Prevention expressed concerns Thursday that it could spread further.
Some experts credit the fast and aggressive response with keeping the number of cases from exploding. There are 98 cases reported in eight states and Mexico, including 82 in California.
There could easily have been many more cases had the outbreak been detected later by health officials.
"If it wasn't for them, we'd have over 2,000 cases by now," said Dr. James Cherry, a UCLA measles expert and primary editor of the Textbook of Pediatric Infectious Diseases. "It's obvious that that hasn't happened, and I think that's because of what the public health people have done."
The measles virus first spread among Disneyland workers and visitors between Dec. 17 and 20. Officials got the first clue of the outbreak about two weeks later when a healthcare provider alerted California public health officials of a possible case of the disease.
The next day, Utah officials reported two suspect cases. By Jan. 5, a Monday, more patients emerged in counties across California.
The common denominator for all patients is that they visited Disneyland during the holiday season — and that's when officials knew they had the makings of a serious outbreak, announced on Jan. 7, said Dr. James Watt of the California Department of Public Health.
The speed in identifying the outbreak's epicenter "made a big difference," said Dr. Matt Zahn, medical director of epidemiology for Orange County.
But there was still a big challenge: More people got sick swiftly. "It makes it harder to control, because there are more cases," he said.
Orange County officials have had to identify more than 1,000 potentially exposed people. "It's incredibly difficult," he said.
In the Salt Lake City area, officials responding to the two initial measles cases among Disneyland guests identified more than 390 people who could have been exposed. Each day, health officials check people off that list. As of Thursday, two were still quarantined.
So far, only one other person in Utah has fallen ill with measles — an unimmunized person already under quarantine before becoming contagious. The same process played out in dozens of other communities across the nation where measles was identified.
In San Diego County, officials immediately shut down and disinfected an urgent care clinic after six measles patients arrived. About 160 people in contact with the patients were interviewed, and 20 were put under quarantine until they could prove they had immunity.
When a boy ill with measles came to school in early January, Orange County officials rushed to review immunization records of students who came into contact with him at Huntington Beach High School and ordered about two dozen students with no proof of immunity to leave campus for three weeks.
In Los Angeles County, interim health officer Dr. Jeffrey Gunzenhauser said officials have identified at least 700 people exposed to the measles virus; 19 have been infected in the county.
"As soon as we reach out to those contacts, we say, 'Have you been vaccinated? Can you verify that to us?'" Gunzenhauser said. "If they aren't vaccinated, we immediately would offer them vaccine if that's appropriate. And if it's helpful, we could also do a test quickly to determine whether they're ... immune or not."
Officials can take steps to protect unvaccinated people if their exposure to the measles virus is known. If caught within three days of exposure, a measles vaccine can provide protection from illness. Within six days of exposure, getting a substance called immunoglobulin — concentrated antibodies extracted from donated blood that boost the immune system — can also protect the patient, Cherry said.
By keeping unvaccinated people at home before they become contagious, "we're protecting them from spreading it to others," Gunzenhauser said.
But there could be improvements. Gunzenhauser said physicians need to do a better job at quickly getting suspected measles cases reported to the public health department; it has been taking more than five days on average to do so.
With the Super Bowl, attention is turning to Arizona's measles situation. Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases, said Thursday she wasn't overly alarmed about the potential risk because she believed most of those at the game will be vaccinated.
But she cautioned that the year was already shaping up to be a serious year for measles. "It's only January, and we've already had a very large number of measles cases — as many cases as we have all year in typical years," she said. "This worries me."