Q:

Should I be concerned about health (bacteria/lice) after having birds fly directly over me?

Yesterday a flock of birds (crows) passed over my head. I've heard that there are many bacteria and lice in the feathers of birds. So I'm thinking about whether to wear or launder the clothes that I wore. What do you recommend I do? Is it ok to wear it again?

A:

The situation and context is of some minor importance: Did you encounter the birds in close proximity, such as startling them from the ground and receive a cloud of dust and feathers as they departed? Did they fly dozens or hundreds of meters overhead?
While it's true that many birds have some population of feather lice (Mallophaga), even in healthy birds, they are harmless to humans.1
All animals, including humans, are hosts to vast populations of bacteria. Of these, the majority are innocuous or even necessary or helpful. That said, microorganisms can be the cause of illness and moreso if they are unfamiliar to your immune system.2
Wild animals can be carriers of disease, and one should always exercise caution when handling or working with animals. Getting bitten, scratched, or even removing a carcass from a roadway, for example, has certain risks associated.
Note that most situations where illness or health problems arise usually involve contact with fluids, breaks in your skin, etc. Our skin and immune systems are remarkably efficient at keeping pathogens out or neutralized. Unless you were in direct contact with the animals and/or were injured in some way, or had a sneeze or excretion come your way, you should be fine. (And even if you were in direct contact you would likely still be fine. An injury such as a scratch from a wild animal should be disinfected and monitored.)
References

Temple, S. A. 2001. Form and Function: The External Bird. In Handbook of Bird Biology (S. Podulka, R. Rohrbaugh, Jr., and R. Bonney, eds.) The Cornell Lab of Ornithology. Ithaca, NY.
https://en.wikipedia.org/wiki/Bacteria

