Delusional infestation (DI) is a rare and bizarre condition. Patients are utterly convinced they are infected with living or inanimate pathogens (think: worms, insects, and fungi) when, in reality, there is nothing there.
It can be debilitating and scary, and now, it appears, more common than previously thought. A report published in JAMA Dermatology estimates that 27.3 people per 100,000 (0.027 percent) suffer from the disorder. This would put the number of people in the US with DI at roughly 89,400.
Reports of DI go back to 1894 when a Parisian dermatologist called Georges Thibierge documented cases of patients falsely believing they had scabies. However, symptoms and causes vary wildly. Bugs are a common culprit. Patients often complain of "crawling" and "biting" sensations. They might also claim pathogens are leaving marks on their skin or building nests.
More recently, there has been Morgellons disease, which was first identified in 2001. Sufferers are convinced there are fibers embedded in their skin, left there by mysterious – possibly alien – creatures that live in the body.
Singer-songwriter Joni Mitchell described it as "this weird incurable disease that seems like it's from outer space... Fibers in a variety of colors protrude out of my skin: they cannot be forensically identified as animal, vegetable or mineral. Morgellons is a slow, unpredictable killer – a terrorist disease. It will blow up one of your organs, leaving you in bed for a year."
But a two-year, half-a-million dollar study led by the CDC found nothing. Doctors say it isn't real.
While DI does not physically harm people in a direct sense, efforts to try and remove the pathogens can be extreme and tend to become more elaborate with time. Aside from frequent cleaning, clothes changing, and bed making, patients may resort to harsh chemicals, gasoline, bleach, and self-mutilation.
We know that people of all ages and gender can be affected, though it is more prevalent among older and middle-aged adults and women outnumber men. A link has also been found between DI and social isolation, but until now there had been no population-based study of DI prevalence.
Researchers used data from the Rochester Epidemiology Project (REP), a collaboration of medical facilities in Wisconsin and Minnesota, to work out exactly how many people from Olmsted Country in Minnesota had the condition. To qualify, patients had to be a resident of the county on December 31, 2010.
Thirty-five patients were identified, of which 13 were men and 22 were women. The mean age at the time of diagnosis was 64.5 years, the majority of whom were white, though this perhaps says more of the homogeneous demographics of Olmsted county than it does of DI prevalence in non-white populations. The researchers say there is not yet enough info to make assessments about the frequency of DI in more diverse communities.
The study also did not specify whether the cases reported were primary DI or secondary DI (which would make it secondary to psychiatric disorders like schizophrenia, drug use, or conditions such as Alzheimer's).
However, the researchers say there is enough data to suggest that DI is currently underreported.