Every once in a while, there's news of a measles outbreak. On the surface, they don't involve large numbers of cases — there's one in Minneapolis right now that has racked up 21 cases so far — and so people seem to wonder why these outbreaks are such a big deal.

Here's one reason why: Measles transmission within the US stopped in 2000 because of vaccination. Outbreaks here start with an importation from somewhere else where the disease still flourishes — but they gain a foothold because lack of vaccination, primarily from vaccine refusal, lets the disease get past what should be an impregnable barrier of herd immunity to attack those who are too young to be vaccinated or whose immunity has faded.

Here's another reason: Stopping the measles virus before it can cause serious disease — and by "serious," I mean deafness, pneumonia, encephalitis and miscarriage — is incredibly costly and labor-intensive. An account published overnight in the Journal of Infectious Diseases gives a glimpse at just how costly. To stop a 14-person outbreak that began with one unvaccinated tourist visiting a US emergency room, the Arizona Department of Health had to track down and interview 8,321 people; seven Tucson hospitals had to furlough staff members for a combined 15,120 work-hours; and two hospitals where patients were admitted spent $799,136 to contain the disease.

Here's how the outbreak unfolded:

In February 2008, a 37-year-old Swiss woman who had never been vaccinated against measles arrived in Tucson after a visit to Mexico. She developed breathing problems and a rash and went to a local hospital's emergency room. They suspected she had a viral illness and admitted her.

Here's what you have to know, to understand what happened next. Measles is extremely contagious; up to 90 percent of unvaccinated people who are exposed to it will get it. And if someone nearby has it, you will get exposed — because coughed-out measles virus can travel across a room, and hangs in the air for hours. The best protection against spreading measles in a hospital is putting someone in a negative-pressure isolation room, which is engineered so no air can leak out into the rest of the hospital. It took two days to get the Swiss tourist into isolation, because measles is rare enough in the US that it was not the hospital personnel's first thought.

Meanwhile:

A 50-year-old woman who had spent an hour in the ER at the same time as the Swiss woman caught the disease from her. Patient 2 got taken care of, went home, and started feeling feverish nine days later. She had difficulty breathing and thought at first she was having an asthma attack, so she went back to the hospital and was admitted for two days. That she had measles would not be discovered until six days after that.

While she was in the hospital, Patient 2 unknowingly infected a 41-year-old health care worker who took care of her — and who was scheduled to get a measles-vaccine booster shot that very day, because the hospital was also caring for the tourist. Patient 2 also passed measles to an unvaccinated 11-month-old boy who was in the same ER while she was waiting to get checked for asthma, and to two unvaccinated siblings — 3 and 5 years old — who were visiting their mother on the same hospital floor after Patient 2 was admitted.

Patient 3, the health-care worker, passed measles to a 47-year-old woman in her emergency department — who later ended up in an intensive care unit with measles pneumonia — and later to a 41-year-old man in his home. Patient 4, the toddler, gave the virus to an unvaccinated 1-year-old while they were both in the same pediatrician's office. Five other people were infected somewhere in their everyday lives: a 2-year-old boy who had never been vaccinated and who also ended up in an ICU with seizures brought on by high fever; a 9-month-old and an 8-month-old, also unvaccinated; and two adults, 35 and 37, who might have gotten one dose as children, but had no documentation of receiving a second dose.

Those 14 are just the confirmed cases. In addition to them, there were 363 suspected ones, and today's paper makes clear authorities believe there were more illnesses than they know. And for every known case, there were dozens or hundreds of exposed people who had to be checked: 145 passengers on the tourist's flight from Mexico, 1,795 patients in the ER that treated Patient 2, 25 people who attended church with Patient 7, 10 kids in the same day care center as Patient 8.

There's an important dimension to this outbreak that may not be evident at first. We tend to blame parents who hold their kids back from vaccination for breaches in the wall of herd immunity. But the people who were infected in this outbreak and shared responsibility for passing it on included adult health care workers who had never been vaccinated and who had missed or declined the chance to get booster shots. By doing that, they put their unknowing patients at risk — and infected, among others, someone with brain cancer and another person living with Down syndrome.

When the hospitals checked to see who among their staff wasn't vaccinated, they found that 30 percent didn't know or couldn't prove it. The two hospitals where measles patients were cared for actually did blood tests on their staff, and found that 9 percent were non-immune: never-vaccinated, never-infected. If the hospitals had not acted to identify those employees and send them home or vaccinate them, they could have hosted a roaring epidemic that might have been impossible to contain.

We can argue endlessly, and do, about people who refuse vaccination for themselves or their children. Under law, they have the right to take that risk. But what this Arizona outbreak makes clear is how many more people are forced to assume that risk without being consulted: not only the infants, elderly and immune-compromised among those 8,321 people exposed in this outbreak, but the hospital shareholders and taxpayers who paid the bill for it to be contained. Until we start counting up those costs as well, we won't achieve an honest accounting of vaccine refusal's true price.

Cite: Chen SY, Anderson S, Kutty PK et al. Health Care–Associated Measles Outbreak in the United States After an Importation: Challenges and Economic Impact. J Infect Dis. (2011) AOP April 28, 2011. doi:10.1093/infdis/jir115

See Also:

Measles/Public Health Image Laboratory/CDC