Concurrent Infection with Murine Typhus and Scrub Typhus in Southern Laos—the Mixed and the Unmixed

Scrub typhus, murine typhus, and spotted fever group rickettsia all occur in the Lao PDR (Laos) [1], [2]. Scrub typhus and murine typhus account for ∼16% and 10%, respectively, of acute undifferentiated fever in blood culture–negative adults admitted to hospital in the capital city, Vientiane [1]. However, typhus-like illnesses are significant diagnostic challenges; patients with leptospirosis, dengue, typhoid, and malaria are also common and can present with similar symptoms and signs. Although these pathogens are common and mixed (or concurrent) infections are expected, the laboratory diagnosis of mixed infection is a vexed subject. Reports of mixed infections often use only serological criteria. The problems of antibody persistence and interspecies cross-reaction raise uncertainty as to whether these results represent true mixed infections, sequential infections, or cross-reactions. We report a patient with concurrent scrub typhus and murine typhus, demonstrated by dual PCR positivity, and discuss evidence for identifying mixed infections.