Salmonella Infection (Salmonellosis) Workup

Updated: Jul 24, 2017
  • Author: Alena Klochko, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Workup

Laboratory Studies

Microbiology

Modern blood culture systems are 80-100% accurate in detecting bacteremia. As the disease duration increases, the sensitivity of blood cultures decreases, while the sensitivity of stool isolation increases.

Freshly passed stool is the preferred specimen for isolation of nontyphoidal Salmonella species. Since stool carriage of S typhi may be prolonged, the interpretation of positive results merits caution, and the diagnosis should be established only when accompanied by clinical findings that are typical of infection. [17]

Bone marrow aspirate and culture is superior to blood culture, since the bacterial concentration in bone marrow is 10 times that of peripheral blood. In patients who received antibiotic therapy prior to hospitalization, bone marrow aspirate may still be positive for Salmonella even if blood culture results are negative. [29]

In cases of typhoid fever, S typhi or S paratyphi may also be isolated from urine, rose spot biopsy, or gastric or intestinal secretions.

Grouping of Salmonella isolates is usually performed with polyvalent antisera specific for O and Vi antigen. S typhimurium belongs to group B; S enteritidis and S typhi belong to group D.

Salmonellosis is a reportable disease in the United States.

Hematology and chemistry

Although the WBC count is usually within the reference range in patients with salmonellosis, approximately one fourth of patients with typhoid fever are leukopenic, neutropenic, or anemic. Thrombocytopenia is neither universal nor diagnostic.

The eosinophil count and sedimentation rate are typically low. A high sedimentation rate suggests abscess formation or osteomyelitis. Eosinophilia should prompt a search for concomitant parasitic infection. [17]

Mild hepatocellular liver function abnormality is common.

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Imaging Studies

Radiologic findings in salmonellosis are nonspecific, and literature reports are scarce. The explanation lies in the fact that most individuals who develop acute Salmonella infection do not seek specialized medical assistance, do not undergo radiographic or endoscopic workup, and, when necessary, are treated empirically but successfully with supportive therapy and broad-spectrum antibiotic therapy. [30]

In a group of 3 patients with Salmonella infection, CT examination by Balthazar et al (1996) showed slight (5-8 mm) symmetrical and homogenous thickening of the wall of the terminal ileum and slight (3-5 mm) circumferential thickening of the cecum and descending colon. In addition, thickening of the sigmoid colon and the wall of the rectum was seen in one case, and small regional mesenteric nodes (< 1 cm) were visualized in another case. [31]

Puylaert et al (1997) reported that ultrasonography might be helpful in differentiating infectious ileocecitis (caused by Salmonella, Yersinia, or Campylobacter) from ileocecal Crohn disease and appendicitis. Among the fairly specific findings that favor an infectious etiology include prominent haustration of cecum and right colon and symmetrical mural thickening of terminal ileum and cecum. [32]

It has been suggested that patients older than 50 years with nontyphoid Salmonella bacteremia should undergo clinical assessments such as computed tomography or magnetic resonance imaging to rule out concurrent vascular infections. [33]

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Other Tests

Serological tests used in the diagnosis of enteric fever yield limited sensitivity and specificity. The Widal test is used to measure antibodies against O and H antigens of S typhi. Newer diagnostic tests (Typhidot, Tubex) allow direct detection of immunoglobulin M (IgM) antibodies against specific S typhi antigens. These tests are promising but need further evaluation in large community settings. [34]

Nested polymerase chain reaction (PCR) using H1-d primers has been used to amplify specific genes of S typhi, with high sensitivity and specificity. This may eventually replace blood culture as the criterion standard. [35]

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