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Nested PCR for Diagnosis of Typhoid Fever

The superiority of the nested PCR employing H 1-d primers over culture or single-dilution Widal (4) should be reevaluated for isolates from unusual sites and from among those coinfected with human immunodeficiency virus (HIV)/AIDS. Numerous extraintestinal complications are known with Salmonella enterica serovar Typhi infection. For example, the involvement of the central nervous system might occur in 3 to 35% of cases, that of the cardiovascular system in 1 to 5% of cases, that of the pulmonary system in 1 to 86% of cases, that of bones and joints in 1% of cases, that of the hepatobiliary system in 1 to 26% of cases, and that of the genitourinary system in 1% of cases in other extraintestinal sites (2). The recommendation to use a single-dilution Widal titer toward confirmation of a specific typhoid diagnosis needs to be reviewed among recipients of different typhoid vaccines. The background serologic response to inactivated vaccine might reduce the utility of a single-dilution Widal test in clinical practice. Furthermore, the serologic response might have been meager among those infected with HIV/AIDS. In India itself, there are estimated to be 5.1 million people infected with HIV, with an overall estimated adult prevalence of below 1%. Both HIV serotype 1 and HIV serotype 2 exist in India, and HIV-1 C is the commonest subtype reported (1). With increased global travel, the previous receipt of a live typhoid vaccine from abroad by a febrile patient undergoing investigations to exclude typhoid might impede the utility of nested typhoid PCR (4). Clinicians in areas where typhoid is endemic might come across several HIV-positive patients who have been vaccinated with live typhoid vaccine prior to travel to these areas (3).