Vi serology in screening of typhoid carriers: improved specificity by detection of Vi antibodies by counterimmunoelectrophoresis

Abstract

SUMMARYA purified soluble Vi antigen was used in counterimmunoelectrophoresis (CIE), passive haemagglutination (HA) and solid phase radio-immunoassay (SPRIA) for detection of serum Vi antibody. Serum Vi antibody was detected in 13 of 14 chronic typhoid carriers by both CIE and HA. SPRIA studies showed that Vi antibodies in sera of these carriers were mainly of the IgG class. Successful treatment with amoxycillin in one carrier, who initially showed a positive Vi test, resulted in a reversion in 6 months to seronegativity as measured by Vi CIE. However, Vi antibody was also detected in 10 sera (3 %) from 329 control subjects by HA but not by CIE. When the CIE assay was applied to 1030 serum specimens obtained from hospitalized patients, it was able to detect one typhoid carrier, but one (0 1 %) non-carrier also gave a positive Vi CIE test. It is thus concluded that Vi CIE is more specific and no less sensitive than Vi HA for the detection of the typhoid carrier state. The finding by SPRIA that the anti-Vi antibodies present in typhoid carriers' sera were mainly of the IgG class further justified the use of CIE as a precipitation test for their detection.

Epidemiology of typhoid fever in Singapore

“…Only one carrier was identified in 12 outbreaks where food handlers were implicated. Combining multiple faecal cultures with some of the reportedly more sensitive methods such as bile sampling with a string capsule device [22] and various Vi antibody serological tests [23][24][25][26][27][28] could well improve the carrier detection rate.…”

Restaurant-associated outbreak of typhoid fever in Maryland: identification of carrier facilitated by measurement of serum Vi antibodies

“…Based upon these limited, although significant, data, we suggest that a level of _15 p.g of Vi antibodies per ml could serve to identify carriers. The value of measuring Vi antibodies in countries with endemic typhoid fever has been established (7,14,15,18,20,22,24). Vi antibody levels in healthy individuals in these countries are higher than those in the United States, probably due to the prevalence of patients convalescent from typhoid fever (7,14,15,18,20,22,24).…”

“…Later, hemagglutination of erythrocytes coated with purified Vi was reported to be a more reliable assay (15,18). Reports of this and other methods confirmed the value of measuring Vi antibodies for identifying carriers (7,8,14,20,22,24). These assays however, did not allow results to be compared between laboratories.…”

Epidemiology and control of an outbreak of typhoid in a psychiatric institution

“…No attempt was made to identify urinary carriers as no such carrier has been reported in the national chronic typhoid carrier registry for the past 10 years, and inclusion of a sample of urine for culture would further strain the limited resources. The sensitivity and specificity of highly purified V'i serology in the detection of chronic typhoid carriers [14,15] have not been established locally. However, it does not detect all the carriers in an outbreak and stool cultures will still be required [16].…”