The "Enteric Fevers" (Typhoid Fever)

The "Enteric Fevers" (Typhoid Fever)
This syndrome is produced by only a few of the salmonellae, of which Salmonella Typhi (typhoid fever) is the most important. The ingested salmonellae reach the small intestine, from which they enter the lymphatics and then the bloodstream. They are carried by the blood to many organs, including the intestine. The organisms multiply in intestinal lymphoid tissue and are excreted in stools.
Bacteremia with Focal Lesions
This is associated commonly with S choleraesuis but may be caused by any salmonella serotype. Following oral infection, there is early invasion of the bloodstream (with possible focal lesions in lungs, bones, meninges, etc), but intestinal manifestations are often absent. Blood cultures are positive.
Enterocolitis
This is the most common manifestation of salmonella infection. In the United States, Salmonella Typhimurium and Salmonella Enteritidis are prominent, but enterocolitis can be caused by any of the more than 1400 group I serotypes of salmonellae. Eight to 48 hours after ingestion of salmonellae, there is nausea, headache, vomiting, and profuse diarrhea, with few leukocytes in the stools. Low-grade fever is common, but the episode usually resolves in 2–3 days.
Inflammatory lesions of the small and large intestine are present. Bacteremia is rare (2–4%) except in immunodeficient persons. Blood cultures are usually negative, but stool cultures are positive for salmonellae and may remain positive for several weeks after clinical recovery.
Diagnostic Laboratory Tests
Specimens
Blood for culture must be taken repeatedly. In enteric fevers and septicemias, blood cultures are often positive in the first week of the disease. Bone marrow cultures may be useful. Urine cultures may be positive after the second week.
Stool specimens also must be taken repeatedly. In enteric fevers, the stools yield positive results from the second or third week on; in enterocolitis, during the first week.
A positive culture of duodenal drainage establishes the presence of salmonellae in the biliary tract in carriers.
Bacteriologic Methods for Isolation of Salmonellae
Differential Medium Cultures
EMB, MacConkey s, or deoxycholate medium permits rapid detection of lactose nonfermenters (not only salmonellae and shigellae but also proteus, serratia, pseudomonas, etc). Gram-positive organisms are somewhat inhibited. Bismuth sulfite medium permits rapid detection of salmonellae which form black colonies because of H2S production. Many salmonellae produce H2S.
Selective Medium Cultures
The specimen is plated on salmonella-shigella (SS) agar, Hektoen enteric agar, XLD, or deoxycholate-citrate agar, which favor growth of salmonellae and shigellae over other Enterobacteriaceae.
Enrichment Cultures
The specimen (usually stool) also is put into selenite F or tetrathionate broth, both of which inhibit replication of normal intestinal bacteria and permit multiplication of salmonellae. After incubation for 1–2 days, this is plated on differential and selective media.
Final Identification
Suspect colonies from solid media are identified by biochemical reaction patterns and slide agglutination tests with specific sera.
Tube Dilution Agglutination Test (Widal Test)
Serum agglutinins rise sharply during the second and third weeks of Salmonella Typhi infection. The Widal test to detect these antibodies against the O and H antigens has been in use for decades. At least two serum specimens, obtained at intervals of 7–10 days, are needed to prove a rise in antibody titer. Serial dilutions of unknown sera are tested against antigens from representative salmonellae. False-positive and false-negative results occur. The interpretive criteria when single serum specimens are tested vary, but a titer against the O antigen of > 1:320 and against the H antigen of > 1:640 is considered positive. High titer of antibody to the Vi antigen occurs in some carriers.