Bird and Bat Droppings and Histoplasmosis

Why this matters

Attics with bat roosts, chimneys, rooftop units under a pigeon perch, barn and outbuilding jobs: these are routine work for roofers, HVAC techs, chimney sweeps, electricians and gutter crews. The droppings in them can carry a fungus that sends healthy adults to the hospital with what looks like pneumonia, and it does so in clusters, because everyone who was on that job breathed the same dust. The protection is mostly water and a respirator. The failure is treating dried guano as dirt and going at it with a scraper, a broom or a leaf blower.

What the hazard actually is

Histoplasmosis is a lung infection caused by Histoplasma capsulatum, a fungus that lives in soil and grows especially well in soil and debris enriched by bird or bat droppings. It produces microscopic spores. Disturb the material and the spores go airborne; breathe them and they settle deep in the lungs.

The bird-versus-bat distinction matters and it is the one most people get wrong:

• Birds (pigeons, starlings, blackbirds, chickens) are not infected themselves, because their body temperature is too high for the fungus. Their droppings feed it. So the risk from birds lives in accumulated, aged droppings, especially where they have mixed into soil, leaves, insulation or roof debris over months or years. A fresh splatter on a condenser lid is a cleaning job; a thick, crusted layer under a long-used roost is the hazard.
• Bats can be infected and shed the fungus in their droppings. Bat guano can carry it even when fresh, and an attic roost concentrates it in a dry, enclosed space with no air movement.

Histoplasma is found across much of the country, with the Ohio and Mississippi River valleys the long-recognized center. CDC has noted that cases turn up well outside those maps, so the honest field rule is that geography raises or lowers the odds but does not clear a job. Two other illnesses ride along with the same material: cryptococcosis, from a yeast common in pigeon droppings, and psittacosis, a bacterial infection from bird droppings and dust. The controls below cover all three because all three are inhalation hazards from disturbed droppings.

Why it hits the healthy tech

Most people in endemic areas have been exposed at some point and never knew; a small breath of spores in ordinary outdoor dust usually causes no illness or a mild one. That is why the hazard gets dismissed. What changes the outcome is dose. A tech scraping guano off attic joists, at face height, in a closed space, for an hour, takes in a spore load no ordinary day delivers, and a large inoculum can make a fit 30-year-old seriously ill. People with weakened immune systems (from chemotherapy, organ transplant drugs, uncontrolled HIV, some arthritis medicines) are at risk of the disseminated form, where the infection spreads beyond the lungs, and should not do this work at all.

Symptoms usually appear 3 to 17 days after exposure: fever, cough, fatigue, chills, headache, chest pain and body aches. It does not spread from person to person. It can look like flu or a bacterial pneumonia, and antibiotics for pneumonia do not treat a fungus, which is why the exposure history matters so much. The only medical instruction this card gives: a tech who develops fever, cough or chest pain within about three weeks of a droppings job gets medical care and names the exposure.

TECH:   Fever and a dry cough since Tuesday. Ten days
        ago I spent three hours in an attic with bat
        droppings. Southern Ohio.
DOCTOR: Respirator?
TECH:   Paper dust mask. It slipped.
DOCTOR: Any other birds or bats lately?
TECH:   Pigeon mess on a rooftop unit the week before.
DOCTOR: Then histoplasmosis is on the list, and a
        couple of the guys on that crew should know.

The useful parts are the material (bat versus bird), the space (attic, enclosed), the duration, the state, what protection actually held, and who else was there. A clinician cannot ask about an exposure they do not know happened.

The controls, in the order they work

NIOSH's guidance for workers, Histoplasmosis: Protecting Workers at Risk, ranks the controls the way any inhalation hazard gets ranked: avoid it, suppress it, then protect the person.

Avoid disturbing it. If the job can be done without walking through, kneeling in or scraping the accumulation, do it that way. Run a new duct on the other side of the attic; replace the condenser lid rather than scraping it on site; access a chimney from the top rather than crawling through a guano-floored attic to reach the thimble.

Wet it before anyone touches it. Water is the suppression method NIOSH describes: a fine mist first, so the spray itself does not blast dry material into the air, then a thorough soak. A pump garden sprayer is the right tool; a hose nozzle on jet is the wrong one. NIOSH discusses chemical disinfection and notes the effective chemicals bring serious hazards of their own, so in trade work, wetting with water is the control. Keep the material wet throughout; it dries fast in a hot attic.

Remove it without making dust. Shovel or scoop wet material into heavy bags. No broom, no shop vac, no leaf blower, no compressed air. A HEPA-filtered vacuum built for hazardous dust is a specialist tool, not a shop vac with a better filter.

Contain it. Close the attic hatch below you, shut down the HVAC system if its return draws from the work area, and do not leave contaminated insulation where the next person walks.

Protect the person. Disposable coveralls with hoods, disposable boot covers, gloves, and a respirator. NIOSH scales the respirator to the job: for brief, small, wetted work a filtering facepiece is the floor; for larger accumulations or enclosed spaces the step-up is a half-face or full-face respirator with P100 filters, and for heavy, prolonged removal a powered air-purifying respirator. A shop that requires any tight-fitting respirator runs a written program under OSHA's respiratory protection standard, 29 CFR 1910.134: medical evaluation, a fit test before first use and annually, and training. With no program, the crew does not do the disturbance work that required one; it goes to a contractor who has one.

Decontaminate leaving. Bag coveralls and boot covers at the exit, do not wear work clothes home or ride in the cab in them, and wash hands and face before eating or smoking.

The bats themselves are not yours to remove

Bats are protected in many states, and several species are federally listed. Excluding them during the maternity season traps flightless young inside to die, which is both a legal problem and a smell problem two weeks later. Cleanup of a roost happens after exclusion, by someone licensed for wildlife where the state requires it. Timing and legality are their own article. See related: Bats in Attics and the Maternity Season. Bats also carry rabies risk, which has its own response. See related: The Animal Bite or Bat Contact Response SOP.

One rule, two jobs

The shop's gate, a default the owner can tune: a trade tech handles droppings only when they can be wetted and bagged in about ten minutes from a position that does not require kneeling, lying or crawling through them. Anything more is a specialist removal. Here is the same gate on two jobs in the same week, in central Indiana.

Job A: pigeon droppings on a rooftop condensing unit. A light commercial roof over a strip of storefronts, with pigeons roosting on the parapet. The unit's top grille carries a crusted patch about 2 ft by 3 ft, and a layer has washed into the gravel at the unit's base. The tech needs to replace the condenser fan motor, which means lifting that grille.

The tech stays upwind, mists the grille and the gravel patch from the garden sprayer, then soaks both. N95 respirator from the shop's program, gloves, eye protection, disposable sleeves. The wet crust is scraped off the grille into a heavy bag, the gravel patch is soaked again and the top inch scooped into a second bag, about eight minutes in all. Both bags are tied and taken down. The fan motor swap proceeds. The gate passes: small, wettable, reachable while standing, done in under the ten minutes.

Job B: bat guano in a farmhouse attic. An HVAC company is quoting a new duct run across the attic of a 1920s farmhouse. With a light from the hatch, the tech sees guano piled along the ridge for about 12 ft, an inch or two deep, and staining across the insulation below it. A few bats are visible in the ridge vent. The duct route crosses directly under the ridge.

There is no way to wet and bag that in ten minutes, and running the duct means kneeling in it. The gate fails. The tech does not enter. The office tells the customer the duct work is on hold pending two things in order: a licensed wildlife operator excludes the bats at a legal time of year, then a remediation contractor removes the guano and the contaminated insulation under NIOSH-level controls. The duct run is booked after written clearance.

What separates them is not how disgusting each looked. It is quantity, enclosure, and whether the work forces the tech's body into the material. Job A had wind, a small wettable patch and a standing reach. Job B had a closed attic, a pile, and a route straight through it.

The failure this prevents is the version of Job B where the tech kneels along the ridge for two hours in a paper dust mask to "just get the duct in," and three people from the crew are in urgent care ten days later with the same chest cold.

How to check you got this right

• Ask a roofer or HVAC tech whether fresh bat droppings are safe because they are fresh. The right answer is no.
• Check that the trucks working roofs and attics carry a pump garden sprayer, heavy bags and disposable coveralls, not just gloves.
• Read last season's job notes for "bats", "guano" or "pigeons" and see whether any of them recorded who entered, for how long and in what respirator. If not, nobody can answer a clinician's question later.

References

• NIOSH, Histoplasmosis: Protecting Workers at Risk (wetting, removal, scaled respirator selection, decontamination)
• CDC, Histoplasmosis: sources, regions, symptoms and 3 to 17 day onset
• OSHA, 29 CFR 1910.134 Respiratory Protection (written program, medical evaluation, fit testing)
• See related: Bats in Attics and the Maternity Season
• See related: The Animal Bite or Bat Contact Response SOP