[Microbiologic diagnosis of typhoid fever: report on an outbreak]

The incidence of typhoid fever has greatly fallen in Spain although sporadic cases and limited outbreaks may be observed. The usefulness of the serum agglutinin studies for the diagnosis of this disease has been questioned by many authors. However, this diagnosis criteria continues to be used in Spain. The usefulness of blood cultures, stool cultures, urinecultures and serological test is herewith compared.

Three groups were prospectively studied: 18 patients with typhoid fever from one single outbreak, 50 blood donors, and 24 patients with other infections. Blood, stool culture, urinecultures and serology (agglutination) were carried out in the first group and in the other two groups serological test were used to determine the cut-off points and study cross reactions.

Blood culture was found to be the most sensitive technique (94%) followed by stool culture (53%). No positive urineculture of seroconvesrion were observed. The cut off points accepted following the study of the donors were 1/160 or greater for the O antigen and 1/320 or greater for the H antigen. Two false positive for the O antigen and 3 for the H antigen were observed in the 24 patients with other infections.

When suspecting typhoid fever, the combined use of blood culture and stool culture is recommended. The usefulness of serological test in our area lays in the observation of seroconversion associated to a compatible clinical picture. Its performance should not being considered as adequate in unspecific febrile syndromes.