Interference by malaria in the diagnosis of typhoid using Widal test alone

A total of 270 febrile patients (130 males and 140 females) aged between 15 and 59 were screened using thick and thin blood film stains for malaria, bacteriologic culture and Widal test for enteric fevers. Sixty (22%) were positive for malaria while 38 (14%) were positive for enteric fevers out of which 16 (26.6%) concomitantly had malaria parasite. Cases without malaria parasite (MP) or enteric fever organism were 172 (63.7%) and classified as pyrexia of unknown origin (PUO). Forty-four were strictly malaria cases out of which 36 (82%) were due to Plasmodium falciparum, and all had antibody Widal titres > or = 160 to 0 antigen while 4 (9%) were due to Plasmodium malariae, 3 (6.8%) were due to P. ovale and 1 (2.3%) was due to P. vivax. Twenty (52.6%) of the 38 patients with enteric fever had typhoid, all had Widal titres > or = 160 to 0 antigen. In all, antibody reaction Widal titres to H antigen were < 20. There was no statistical significant difference [chi2 = 327.2, P > 0.05] between Widal titres of malaria and typhoid cases. Hence using Widal test alone, one cannot differentiate typhoid fever from malaria. In another 250 healthy adults, of equal sex distribution, used as controls 12 (4.8%) had malaria parasite and 4 (1.6%) had enteric fever organisms. While only 4 (1.6%) gave Widal titre of 80 to 0 antigen the rest had antibody titres of < 20 to O antigen. Malaria could interfere with serological diagnosis of typhoid and hence lead to over diagnosis of typhoid in Nigeria.