False positive malaria rapid diagnostic test in returning traveler with typhoid fever

Abstract

Background: Rapid diagnostic tests play a pivotal role in the early diagnosis of malaria where microscopy or polymerase chain reaction are not immediately available.

Case presentation: We report the case of a 39 year old traveler to Canada who presented with fever, headache, and abdominal pain after visiting friends and relatives in India. While in India, the individual was not ill and had no signs or symptoms of malaria. Laboratory testing upon his return to Canada identified a false positive malaria rapid diagnostic (BinaxNOW® malaria) result for P. falciparum with coincident Salmonella Typhi bacteraemia without rheumatoid or autoimmune factors. Rapid diagnostic test false positivity for malaria coincided with the presence or absence of Salmonella Typhi in the blood.

Conclusions: Clinicians should be aware that Salmonella Typhi infection may result in a false positive malaria rapid diagnostic test. The mechanism of this cross-reactivity is not clear.

Figure 1

Photograph of BinaxNOW® malaria RDT result from Day 37 showing a positive band at position T1 corresponding to P. falciparum infection. The photograph is contrast enhanced to ensure the bands can be seen by the reader.

Figure 2

Denistometry of the control band (leftmost peak) and T1 band (second peak) showing a signal present compared to the background for the RDT result. The y-axis measures pixel intensity versus the distance on the RDT strip. Densitometric analysis was performed using NIH Image J software (http://rsb.info.nih.gov/ij/) [5].