Leptospiral pneumonia.

Leptospirosis, a spirochetal infection, causes a wide spectrum of disease ranging from asymptomatic infection, or influenza-like symptoms, to severe jaundice and renal failure. Humans become infected through skin or mucous membrane contact with infected animal urine or urine-contaminated water or soil. The most common source of human infection worldwide is rats. However, in the United States, dogs, livestock, wild mammals, and cats are also sources. Once leptospires penetrate mucous membranes or breaks in the skin, they disseminate to all parts of the body. Five to ten percent of those infected will have severe leptospirosis with jaundice, known as Weil's disease. The classical presentation of leptospirosis is that of a biphasic illness. The initial septicemic phase lasts 4 to 7 days and is characterized most commonly as a mild influenza-like illness. During the secondary immune phase, leptospires disappear from the blood and cerebrospinal fluid. However, circulating antibodies cause immune-mediated meningitis, uveitis, rash, and, very rarely, circulatory collapse associated with Weil's disease. Pulmonary involvement occurs in 20% to 70% of patients. The more severe pulmonary manifestations are rare. Although attempts should be made to isolate leptospires from the blood or cerebrospinal fluid, the diagnosis is usually established by serologic tests. The effectiveness of antimicrobial therapy in treating leptospirosis has been difficult to assess because of the high variability of the disease's clinical course, although in severe cases, antibiotic therapy is effective even when treatment is delayed. Prevention is difficult because it is almost impossible to eliminate the large animal reservoir of infection.