Person-to-person transmission can occur within families; hospital-associated cases comprise 25% of cases. The median incubation period is 5 days (range, 2–14) with themean age of 50 (range 9 months to 99 years) and 65% occurring among men. Over 90% of patients have an underlying medical condition, including diabetes mellitus (68%), hypertension (34%), or chronic heart or kidney disease. Those with diabetes, kidney disease, chronic lung disease, or other immunocompromising conditions likely are at
highest risk for severe disease.
Camels appear to be the principal reservoir, and several studies show that contact
with dromedary herds of camels is greater among cases than controls. Raw camel milk
is considered a potential source. Persons who work with camels are more likely to have
antibody evidence of past infection.