Diagnosis of leptospirosis.

Sir,

We read with interest the recent article on diagnosis of leptospirosis by Chaudhry et al1. The authors noted that “Seropositive and seronegative patients revealed no significant difference in clinical features and laboratory parameters” and also mentioned for co-infection with other tropical infections1. This report indicates the importance of specific laboratory testing for confirmation of leptospirosis. In fact, several tropical infections share common presentations with leptospirosis and the concurrent infection is also possible. Therefore, there is no process to rule out the possible concurrent infection and Chaudhry et al1 also accepted that there were many cases with co-infections. Hence, the observed clinical features and laboratory parameters might be the result of a mixed infection, at least in some cases.

The conclusion that seropositivity has no relationship to clinical features and laboratory parameters must be carefully considered. The practitioner has to realize the limitation of presently available laboratory tests and the source of error in diagnosis2. For the widely used serological test, the important concern is on the cross-reactivity with other infections (such as syphilis and borreliosis3. The difference in diagnostic property can be observed in various diagnostic serological test kits available4. Additionally, the limitation of diagnosis can be expected in the acute phase of the disease due to lack of antibodies2. It has been shown that different laboratories in different clinical settings give different rates of accuracy in diagnosis5. Also, within an institute, the error due to specimen collection in pre-analytical phase can be expected6. Hence, the new technique based on molecular test is developed and available for clinical usage in some clinical settings. Nevertheless, for molecular diagnosis, the cost and availability are the main obstacles in real clinical practice in developing countries2.