An unusual H antigen (Z66) in strains of Salmonella typhi.

Eleven Salmonella typhi isolates were recovered from patients with typhoid in Indonesia. These motile isolates had neither H:d nor H:j antigen but had a new H antigen, designated Z66 in this paper. After passage through semi-solid agar medium with anti-Z66 serum (in U-tube), 7 strains were agglutinable by H:d antiserum. No strain was able to express the three H factors. In case of typhoid fever caused by such strains, conventional Widal test may not detect anti-H:d agglutinins in patients' sera.