Lice were prevalent in a sample of 203 homeless people in San Francisco, as were Bartonella quintana infections, which cause trench fever, according to a recent study (Bonilla DL et al. Emerg Infect Dis. 2014;20:1645-1651).
Lice are vectors of B quintana, which they transmit by excreting bacteria-laden feces onto human skin. The bacteria enter the body through mucous membranes or a louse bite. Trench fever causes symptoms such as severe headache, conjunctival congestion, lymphadenopathy, and relapsing fever, as well as potentially life-threatening endocarditis and bacillary angiomatosis. Lice also can cause pruritus, infections from scratching, and anemia. Dirty clothing and close contact with others create an ideal environment for lice infestations and transmission, making homeless people an especially vulnerable population.
Lice-borne Diseases in the Homeless Population. JAMA. 2014;312(19):1962. doi:10.1001/jama.2014.14764