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Salmonella Typhi infection (Salmonella enterica serotype Typhi)
2019 Case Definition

NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Surveillance case definitions are not intended to be used by healthcare providers for making a clinical diagnosis or determining how to meet an individual patient’s health needs.

CSTE Position Statement(s)

  • 18-ID-08

Background

S. Typhi are bacteria that often cause a potentially severe and occasionally life-threatening bacteremic illness. While fever and gastrointestinal symptoms are common, the clinical presentation varies, including mild and atypical infections. In the United States, approximately 300 cases of typhoid fever are reported each year, 85% of which are acquired during international travel. Ongoing surveillance of S. Typhi infections is essential to detect and control outbreaks, determine public health priorities, monitor trends in illness, and assess effectiveness of public health interventions.

Clinical Description

Infections caused by Salmonella enterica serotype Typhi (S. Typhi) are often characterized by insidious onset of sustained fever, headache, malaise, anorexia, relative bradycardia, constipation or diarrhea, and non-productive cough. However, mild and atypical infections may occur. Carriage of S. Typhi may be prolonged.

Clinical Criteria

One or more of the following:

  • Fever
  • Diarrhea
  • Abdominal cramps
  • Constipation
  • Anorexia
  • Relative bradycardia

Laboratory Criteria for Diagnosis

Confirmatory laboratory evidence:

  • Isolation of S. Typhi from a clinical specimen.
Presumptive laboratory evidence:
  • Detection of S. Typhi in a clinical specimen using a culture-independent diagnostic test (CIDT).
Note: Serologic testing (i.e., detection of antibodies to S. Typhi) should not be utilized for case classification.

Epidemiologic Linkage

  • Epidemiological linkage to a confirmed S. Typhi infection case, OR
  • Epidemiological linkage to a probable S. Typhi infection case with laboratory evidence, OR
  • Member of a risk group as defined by public health authorities during an outbreak.

Criteria to Distinguish a New Case from an Existing Case

A new case should be created when a positive laboratory result is received more than 365 days after the most recent positive laboratory result associated with a previously reported case in the same person.

Case Classification

Probable

  • A clinically compatible illness in a person with presumptive laboratory evidence.
  • A clinically compatible illness in a person with an epidemiological linkage.

Confirmed

A person with confirmatory laboratory evidence

Comments

Several serological tests have been developed to detect antibodies to S. Typhi. However, no current serological test is sufficiently sensitive or specific to replace culture-based tests for the identification of S. Typhi infections. Whether public health follow-up for positive serologic testing is conducted and how is at the discretion of the jurisdiction.

It is estimated that approximately 2-5% of persons infected with S. Typhi become chronic intestinal carriers who continue to shed S. Typhi for more than one year. These people are typically referred to as chronic carriers.

Differentiating whether a person is a chronic carrier or is experiencing a new infection often relies on a variety of factors, including advanced laboratory testing (e.g., pulsed-field gel electrophoresis [PFGE], whole genome sequencing [WGS]) to compare the isolate from the previous infection to the new isolate. While these methodologies can provide detailed information about the genetic make-up of the organisms, there is still significant variability in how two organisms can be defined as different. Given the potential for inconsistent application of the label “different” across jurisdictions, this case definition does not exclude persons with a previously reported S. Typhi Infection case from being counted as a new case if the subsequent positive laboratory result is more than 365 days from the most recent positive laboratory result associated with the existing case.



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