Iowa mumps epidemic--update and additional history

I attended a lecture yesterday given by Patty Quinlisk, Iowa's state epidemiologist. The bad news: there have been over 500 reported cases of mumps as of Monday, April 10, with more cases in neighboring states (30-50 in Nebraska, for example). She did, however, give a bit more history on the epidemic, described below.

The outbreak can be traced back to last December, when 2 cases were found to be IgM-positive for mumps. (IgM is the first type of antibody produced to a new infection; therefore, this is diagnostic of a current infection, whereas looking at a different type of antibody--IgG--shows a prior exposure). In January 2006, an unrelated case of mumps was cultured at the state hygienic laboratory. These weren't exactly surprising; Iowa generally has around 5 cases of mumps every year, and most occur in winter, so 3 in 2 months' time was about normal. However, cases continued to roll in, and in mid-February active surveillance was begun in 7 Iowa counties. So far, there's no signs yet of the epidemic slowing.

Again, mumps is often thought of just as a mild childhood disease, but as with any pathogen, the larger the number of infections, the greater the potential for a serious manifestation of disease to occur. In the case of the current epidemic, there is at least one potential case of encephalitis, a swelling of the brain that can lead to permanent impairment. Mumps is also notorious for causing testicular swelling ("orchitis") in pre-pubescent males. This can manifest in up to 30-40% of male cases, and has the potential for permanent consequences (luckily, rare). Women aren't off the hook, either: infection with mumps during the first trimester of pregnancy results in spontaneous abortion in 20-25% of such pregnancies. Indeed, the virus can be totally asymptomatic in a similar number of patients--but as I mentioned with chicken pox, it's a mistake to dismiss it as "just a mild childhood infection."

Currently, officials are recommending that patients with the mumps isolate themselves for at least 5 days following the onset of symptoms in an effort to stem the epidemic. No other measures (such as quarantine of exposed individuals) have been put in place yet, and it's hoped they won't be necessary.

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What's up with the 68% vaccinated becoming infected? These are relatively old patients (median age 21 yr), , but I thought the mumps vaccine should still be good. Has the mumps strain been tested to see if it's mutated away from vaccine sensitivity?

I discussed that a bit in this comment to a previous thread. I'll re-post portions of a ProMed email:

Follow-up reports have been completed on 154 cases. Of those, 68 percent occurred in people who had received the recommended 2 doses of the measles-mumps-rubella (MMR) vaccine. Iowa, according to Harris, is a state with a high vaccination rate, and she anticipates the majority of mumps infections will occur in people who are considered safe on the basis of their immunization records. "But we know the vaccine doesn't work in everyone," she said. Harris said published data suggest that the vaccine failure rate for mumps is about 5 percent. "So by my estimate, there are about 200 000 people in Iowa who have received the recommended vaccinations but who have no immunity to mumps."

Most likely it's hitting those who were vaccinated, but are part of the 5+% where the vaccine failed.

As far as the strain, strain testing wasn't finished, but it sounds as if the one circulating shouldn't be a problem--it should be close to the vaccine isolate.

I agree with the statement that mumps isn't just a childhood illness. I had mumps when I was an senior undergrad. It was ghastly, not only because eating was very painful, but afterwards I got mild depression for about a month. Not the best time to be ill or depressed; let alone both. Also aren't childhood illness worse in adults? Which is to do with the fact that adult immune systems are mature? Or is that just an urban myth.

I don't know if I had a vaccination as a child. As the British Health Service was pretty good about vaccinations, I may be one of those for whom the vaccination didn't work. I did have a vaccination against whooping cough and then proceeded to catch it years later. My doctor said that it wasn't a very effective vaccination, but the symptoms were less than if I hadn't been injected.

Interestingly when I went for my green card, I didn't have a copy of my vaccination record, so I had to have an MMR vaccination; despite having had both mumps and rubella. Hopefully, I am safe from measles ;)

I am one of those persons who, despite having had all my vaccinations, has no antibodies against mumps. I had measles as a young child, also rubella, but not mumps. When I went back to college for my MS degree at age 35 I had to have another MMR, and even after that my titers are still 0. (I reacted the same way to the HepB vaccine--I'm a nurse and it was required by one hospital I worked at--I had the series of 3 vaccines and never developed antibodies.) I just wish I'd develope the immunities.

For Lab Cat--yes, at least one childhood disease is worse in adults. Chicken Pox can be a killer, especially in a pregnant woman--it can kill her and/or the baby in utero. It can lead to recurring shingles.

I don't know much about measles or mumps except what Tara has posted above. Haven't seen either one in an adult in my medical experience.

Does anyone know if the original people who caught the disease were vaccinated? I would hope so, since they were traveling abroad, but you never know.

Does anyone know if the original people who caught the disease were vaccinated? I would hope so, since they were traveling abroad, but you never know.

We don't know the "index cases"--who truly were the first people to start the epidemic. Since mumps can be spread even by people who are infected asymptomatically, we may never really know.

Hi Tara: Do you know of any way to measure how infectious one virus is compared to another one? For example, can you say regular seasonal flu is more infectious than mumps, which is more infectious than SARS? And by how much?

The mumps outbreak seems almost like a made-to-order rehearsal for a potential pandemic flu, particularly with the role played by airplanes.

The CDC has a list of nine flights whose passengers were likely exposed to mumps. Apparently two infected people did a lot of travelling recently--Spring Break?--and that what's behind the sudden spread. The MMWR article is at

Hi Christine,

That's usually done retrospectively, by examination of how many cases of disease people spread to others (how many "secondary cases" result from each initial case, in other words--R in epidemiological notation). This takes a lot of careful contact tracing, which isn't a very easy thing to do. For one, all of the diseases mentioned can be asymptomatic, but asymptomatic carriers can still spread the organism--which makes it all much messier. A highly vaccinated population also complicates things. So long story short, yes, we can measure how infectious they are, but there's a lot of wiggle room and uncertainty in these measurements, and different strains of the same species of microbe can give vastly different measures of infectivity. (For example, R for "influenza" varies by strain--for H5N1 it's been essentially zero; for other strains it's estimated at between ~1.5-3 generally. That link gives measles infectivity as a range from 10-15. I believe mumps is between the two--higher than influenza, but significantly lower than measles.

The mumps outbreak seems almost like a made-to-order rehearsal for a potential pandemic flu, particularly with the role played by airplanes.

Yep. I just want to emphasize, though, that the air travel was recent--March 26-April 2. (Spring break here was a few weeks earlier--not sure if the other state universities were at the same time). So that can explain the spread of the outbreak to neighboring states, but not its initial origin (which remains cloudy).

"Most likely it's hitting those who were vaccinated, but are part of the 5+% where the vaccine failed".

It's not convincing nor probable to say the 68% 2 dose vaccine reciprients have vaccine failure in this outbreak.
Where is the cross protection?

Why is that neither "convincing nor probable?" We're still talking a small number of cases here--certainly several hundred of the 2 dose recipients would still lack immunity. And if there was no immunity in the first place, speaking about cross-protection is a non-sequitur: there was no protection to "cross."