U.S

A family vacation to Costa Rica turned sour after 12 of 13 relatives developed symptoms of a fungal lung infection following an excursion through bat-filled caves.

In season two of The Last of Us, the cordyceps fungus—spoiler alert—becomes airborne, meaning the fungal infection can spread not just through bites but also when humans inhale its spores. While the TV show is highly fictitious, airborne fungi are most certainly not. A U.S. family now knows this better than most, since 12 of their members became ill after touring a bat cave in Costa Rica.

In a paper published Thursday in the journal Morbidity and Mortality Weekly Report, researchers described 12 confirmed or probable cases of histoplasmosis: a pulmonary infection caused by inhaling the fungus Histoplasma capsulatum. This fungus lives in soil, frequently alongside bird or bat droppings, and can become airborne if the earth is disturbed. While symptoms are usually subtle, the infection can make infants and immunocompromised people vulnerable to more serious illnesses.

During a vacation to Costa Rica in December of last year, 12 of 13 family members toured the bat-colonized Venado Caves, an ancient cave system and popular tourist destination. This essentially meant crawling through bat poop for two hours. When they returned to the U.S., everyone—except the one family member who hadn’t toured the cave—became ill to varying degrees, with symptoms including fever, headache, muscle pain, night sweats, respiratory problems, and gastrointestinal issues.

Five family members sought medical attention. Doctors tested four of them for fungal infections, and two tested positive for histoplasma. Two of the patients also had abnormal chest X-rays, one of which raised concern for possible lung cancer. After learning about their spelunking expedition, healthcare providers notified the CDC, which launched an investigation. Notably, the cave they had visited had also likely caused a histoplasmosis outbreak in 1998 and 1999.

“Antigen testing for all four patients occurred within 1 month of symptom onset, the optimal time frame,” the team, led by CDC researchers, wrote in the report. “However, because antigen detection sensitivity for histoplasmosis is lower in patients with mild disease who are immunocompetent, the negative test results might have been false negatives.” In other words, given that it’s harder to detect histoplasmosis in healthy patients, the family members who tested negative might still have had histoplasmosis.

Ultimately, doctors confirmed that one family member had histoplasmosis, eight members probably did, and three were suspected of having it. Fortunately, none of them became zombies—or had lung cancer—and within 28 days of exposure, they were all on their way to recovery. While doctors usually prescribe antifungal medication for patients with severe histoplasmosis, many cases in healthy individuals go away on their own.

Histoplasmosis is sometimes difficult to diagnose. As such, the researchers urge clinicians to “consider fungal illness in the differential diagnosis of patients with constitutional or pulmonary signs or symptoms after recent caving or other activities associated with risk for histoplasmosis,” they concluded. In collaboration with the U.S. Embassy in Costa Rica and the Costa Rica Ministry of Health, the CDC hopes to see the risk of histoplasmosis included in the Venado Caves tour waiver forms.

It’s not surprising that The Last of Us is so popular. After all, Andrzej Sapkowski—author of The Witcher—wrote that “there’s a grain of truth in every fairy tale.” That seems to hold true, even in a fungal zombie apocalypse.

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