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The MTBDRsl assay (Hain Lifescience GmbH, Germany) is a new line probe assay for the detection of extensively drug-resistant tuberculosis (XDR TB). The test simultaneously detects resistance to ethambutol, aminoglycosides/cyclic peptides, and fluoroquinolones through detection of mutations in the relevant genes. The assay format is identical to the MTBDR Hain assay. The assay was evaluated for the detection of second-line-drug resistance in Vietnamese isolates using two sample sets from the microbiology department of Pham Ngoc Thach Hospital, Ho Chi Minh City, Viet Nam, with existing conventional phenotypic drug susceptibility results for second-line drugs: 41 consecutive fluoroquinolone-resistant isolates and 21 consecutive multidrug-resistant but fluoroquinolone-sensitive isolates. The sensitivity for detection of fluoroquinolone resistance was 75.6% (31/41) (95% confidence interval [95% CI], 59.7% to 87.6%), and for kanamycin resistance, the sensitivity was 100% (5/5) (95% CI, 47.8% to 100%). The sensitivity of the test for detection of ethambutol resistance was low, consistent with previous reports, at 64.2% (34/53) (95% CI, 49.8% to 76.9%). The specificity of the test was 100% for all three drugs. These data suggest that the MTBDRsl assay is a rapid, specific test for the detection of XDR TB but should not be used exclusively to "rule out" second-line-drug resistance. Further operational evaluation is required and should be integrated with evaluations of the MTBDR test.

PCR-restriction fragment length poymorphism (PCR-RFLP) is a simple, robust technique for the rapid identification of isoniazid-resistant Mycobacterium tuberculosis. One hundred consecutive isolates from a Vietnamese tuberculosis hospital were tested by MspA1I PCR-RFLP for the detection of isoniazid-resistant katG_315 mutants. The test had a sensitivity of 80% and a specificity of 100% against conventional phenotypic drug susceptibility testing. The positive and negative predictive values were 1 and 0.86, respectively. None of the discrepant isolates had mutant katG_315 codons by sequencing. The test is cheap (less than $1.50 per test), specific, and suitable for the rapid identification of isoniazid resistance in regions with a high prevalence of katG_315 mutants among isoniazid-resistant M. tuberculosis isolates.

Using an enzyme-linked immunosorbent assay we demonstrate that, in adult patients with typhoid fever, the sensitivity of a serological test based on the detection of anti-lipopolysaccharide immunoglobulin G is increased when used with paired serum samples taken 1 week apart.

Currently, the laboratory diagnosis of typhoid fever is dependent upon either the isolation of Salmonella enterica subsp. enterica serotype Typhi from a clinical sample or the detection of raised titers of agglutinating serum antibodies against the lipopolysaccharide (LPS) (O) or flagellum (H) antigens of serotype Typhi (the Widal test). In this study, the serum antibody responses to the LPS and flagellum antigens of serotype Typhi were investigated with individuals from a region of Vietnam in which typhoid is endemic, and their usefulness for the diagnosis of typhoid fever was evaluated. The antibody responses to both antigens were highly variable among individuals infected with serotype Typhi, and elevated antibody titers were also detected in a high proportion of serum samples from healthy subjects from the community. In-house enzyme-linked immunosorbent assays (ELISAs) for the detection of specific classes of anti-LPS and antiflagellum antibodies were compared with other serologically based tests for the diagnosis of typhoid fever (Widal TO and TH, anti-serotype Typhi immunoglobulin M [IgM] dipstick, and IDeaL TUBEX). At a specificity of > or =0.93, the sensitivities of the different tests were 0.75, 0.55, and 0.52 for the anti-LPS IgM, IgG, and IgA ELISAs, respectively; 0.28 for the antiflagellum IgG ELISA; 0.47 and 0.32 for the Widal TO and TH tests, respectively; and 0.77 for the anti-serotype Typhi IgM dipstick assay. The specificity of the IDeaL TUBEX was below 0.90 (sensitivity, 0.87; specificity, 0.76). The serological assays based on the detection of IgM antibodies against either serotype Typhi LPS (ELISA) or whole bacteria (dipstick) had a significantly higher sensitivity than the Widal TO test when used with a single acute-phase serum sample (P < or = 0.007). These tests could be of use for the diagnosis of typhoid fever in patients who have clinical typhoid fever but are culture negative or in regions where bacterial culturing facilities are not available.

Multidrug-resistant Salmonella enterica serotype Typhi isolates from four outbreaks of typhoid fever in southern Vietnam between 1993 and 1997 were compared. Pulsed-field gel electrophoresis, bacteriophage and plasmid typing, and antibiotic susceptibilities showed that independent outbreaks of multidrug-resistant typhoid fever in southern Vietnam are caused by single bacterial strains. However, different outbreaks do not derive from the clonal expansion of a single multidrug-resistant serotype Typhi strain.

The diagnostic value of an acute-phase single-tube Widal test for suspected typhoid fever was evaluated with 2,000 Vietnamese patients admitted to an infectious disease referral hospital between 1993 and 1998. Test patients had suspected typhoid fever and a blood culture positive for Salmonella typhi (n= 1,400) or Salmonella paratyphi A (n = 45). Control patients had a febrile illness for which another cause was confirmed (malaria [n = 103], dengue [n = 76], or bacteremia due to another microorganism [n = 156] or tetanus (n = 265). An O-agglutinin titer of >/=100 was found in 18% of the febrile controls and 7% of the tetanus patients. Corresponding values for H agglutinins were 8 and 1%, respectively. The O-agglutinin titer was >/=100 in 83% of the blood culture-positive typhoid fever cases, and the H-agglutinin titer was >/=100 in 67%. The disease prevalence in investigated patients in this hospital was 30.8% (95% confidence interval, 26.8 to 35.1%); at this prevalence, an elevated level of H agglutinins gave better positive predictive values for typhoid fever than did O agglutinins. With a cutoff titer of >/=200 for O agglutinin or >/=100 for H agglutinin, the Widal test would diagnose correctly 74% of the blood culture-positive cases of typhoid fever. However, 14% of the positive results would be false-positive, and 10% of the negative results would be false-negative. The Widal test can be helpful in the laboratory diagnosis of typhoid fever in Vietnam if interpreted with care.

The rate of multiple-antibiotic resistance is increasing among Salmonella enterica serovar Typhi strains in Southeast Asia. Pulsed-field gel electrophoresis (PFGE) and other typing methods were used to analyze drug-resistant and -susceptible organisms isolated from patients with typhoid fever in several districts in southern Vietnam. Multiple PFGE and phage typing patterns were detected, although individual patients were infected with strains of a single type. The PFGE patterns were stable when the S. enterica serovar Typhi strains were passaged many times in vitro on laboratory medium. Paired S. enterica serovar Typhi isolates recovered from the blood and bone marrow of individual patients exhibited similar PFGE patterns. Typing of S. enterica serovar Typhi isolates from patients with relapses of typhoid indicated that the majority of relapses were caused by the same S. enterica serovar Typhi strain that was isolated during the initial infection. However, some individuals were infected with distinct and presumably newly acquired S. enterica serovar Typhi isolates.