Bats, pack overnighters, hollow trees, geocaching, and histoplasmosis. I bet you are wondering what they have in common. In this case, 23 participants at a pack overnighter contracted histoplasmosis. Histoplasmosis is an infection caused by a fungus known as Histoplasmosis capsulatum that is commonly found in soil enriched by bird and bat droppings.

One of the activities for the overnighter was to find a geocache buried near a hollow tree. Much digging was done to uncover the cache and there were reports of a white cloud when the cache was opened. All individuals who were geocaching reported respiratory symptoms, and several were hospitalized about three weeks after the campout.

Once histoplasmosis was diagnosed, the state public health office’s infectious disease team came to camp, took soil samples near the tree, and identified a bat colony calling the tree home. One sample tested positive for the fungus.


  1. Do not dig in, work, or use soil that is in the same location as bats or that contains bird droppings.
  2. Avoid exposure during geocaching by keeping the cache clean and above ground.
  3. Bat guano is a common source of the fungus that causes histoplasmosis. Identifying wildlife exposure for diseases can help prevent the illness.


  • Participants with weakened immune systems or some chronic diseases have a higher risk for developing a severe form of histoplasmosis. These individuals should discuss their conditions with their health-care provider.
  • Be mindful of key risk areas including areas where large amounts of bird or bat droppings are common, such as trees, chicken coops, caves, rock crevices, old buildings, and under bridges.
  • Avoid disturbing areas where histoplasmosis is suspected, as the fungus could become airborne.