Serological Diagnosis for Infectious Diseases: Not As Easy as It Appears ! / Lao Medical Journal

ABSTRACT

Serological diagnoses for infectious diseases such as those based on disease¬specific IgM antibody detection often confuse clinicians and therefore make treatment decisions difficult. This is due to the relatively long persistence of IgM in the blood circulation following exposure to the organism or nonspecific polyclonal activation of memory cells. We report a Lao patient diagnosed as having scrub typhus on admission based on detection of IgM to Orientia tsutsugamushi and initially treated with Doxycycline. The patient became afebrile but had severe pulmonary involvement. The blood culture was subsequently positive for Leptospira spp. which is the cause of leptospirosis. The admission blood sample of the patient was negative for Orientia tsutsugamushi, Rickettsia typhi, and Rickettsia spp. DNA targets, by PCR, suggesting that the patient did not have scrub typhus, murine typhus or Spotted Fever. After one week of IV ceftriaxone treatment, the patient improved and was discharged well. The positive IgM to scrub typhus detected on admission was probably due to previous exposure to O. tsutusgamushi, and scrub typhus was not the cause of her presenting illness. Fortunately, Doxycycline, given to the patient for scrub typhus treatment, is also effective for leptospirosis preventing death. However, the patient required intravenous ceftriaxone (which would not have been effective for scrub typhus) when she developed severe disease. This patient’s illness is a reminder that clinicians should be cautious about serological diagnosis. At present, laboratory diagnosis of leptospirosis remains a big challenge for the clinicians because the existing gold standard test such as Microscopic Agglutination Test (MAT) and culture are labour intensive, expensive and seldom available. Until the development of the simple, rapid, and more reliable tests, the empirical treatment of patients with suspected leptospirosis with doxycycline, penicillins or ceftriaxone are strategies to reduce severe complications and death although it should be born in mind that penicillins and ceftriaxone will not be effective against rickettsial organisms.