Here are the details of their analysis. Between 1979 and 2009:

To the right, you can see a breakdown of 141 of the cases they analyzed, broken down by year of diagnosis and also by state where the case was discovered. (They are looking at 141, not 162, because they did not analyze multiple cases from the same donor.) You can see that the trend line is rising — and also where transfusion cases were found outside of the seven endemic states in the Northeast and upper Midwest.

The researchers say:

The 162 transfusion-associated cases we enumerated undoubtedly represent a fraction of those that occurred. The extent to which cases were not detected, investigated, or reported (to the CDC, to other public health authorities, or in publications) is unknown, both in general and with respect to periods, regions, and various case characteristics and outcomes. As underscored by the incidental diagnosis of Babesia infection, even severe cases in babesiosis-endemic regions can be missed or misdiagnosed, not just cases that are asymptomatic or mild or that occur in other U.S. regions. Even if a case is diagnosed, a transfusion investigation might not be considered, conducted, completed, or conclusive… Our findings underscore the year-round vulnerability of the U.S. blood supply—especially, but not only, in and near babesiosis-endemic areas.

Why is this happening?

Some details first about the organism: Babesia microti (and the related B. duncani) are parasites that take up residence in red blood cells. One prominent researcher, not part of this paper, has called it “America’s malaria” – and like malaria, it causes flu-like chills and fever, and so is often ignored or misdiagnosed. But, also like malaria, it can cause anemia, organ failure and death.

Exactly how much babesiosis is there in the US? That’s hard to say. Public health authorities have perceived the risk growing for several years, but it was only this past January that the illness became a reportable disease — meaning that, if a physician diagnoses it in a patient, he or she is supposed to pass news of the case up the hierarchy to a state health department, who pass it on to the CDC.

Since the parasite travels in red blood cells, you can see how it might be a transfusion risk. But just how much of a risk it poses, and what to do about it, has been sparking sharp debate for a number of years. (Here are the minutes from an FDA meeting in 2008, and an FDA summary of the issue from 2010.) The American Association of Blood Banks declared babesiosis in blood a top priority back in 2009.

At the moment, potential donors get asked: “Have you ever had babesiosis?” But most people don’t know the illness exists, and because it can be asymptomatic, people can be infected and not know it.

Moreover, babesiosis isn’t something you can diagnose by looking at a blood donor.  If  someone is infected and experiencing symptoms, those symptoms are likely to be nonspecific — so what might indicate babesiosis might also indicate flu, or a cold, or a number of viral illnesses. But if you ruled out blood donors on the possibility they might have a cold, you’d quickly cut the US blood supply to unsustainable levels.

The problem might be solved if there were a test that could detect Babesia in a blood sample. Right now, there is not. To authorize a test, the FDA needs for a company to bring one forward.  Yet so far, babesiosis is not so widespread that it would guarantee enough sales to justify a test’s R&D costs, and thus no pharmaceutical company has volunteered to develop one. In a companion editorial to the paper released today, Dr. David Leiby of the American Red Cross’s Holland Laboratory says this must change:

What is not acceptable, however, is the status quo. With reports of 162 transfusion-associated cases of babesiosis probably representing only a fraction of actual cases and a potential causal or contributory role for babesiosis in the deaths of B. microti–infected blood recipients, the time to act is now.

Update: Reuters reports on a new paper in Pediatrics describing seven preemies in a neonatal intensive care unit who were infected via two units of contaminated blood. The abstract says five had mild infections but “double-volume exchange blood transfusion with prolonged multidrug treatment was required for the 2 most severe cases.”
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