STEC are estimated to cause more than 265,000 illnesses each year in the
United States. STEC can cause illness that ranges from mild diarrhea to bloody
diarrhea and life-threatening hemolytic uremic syndrome (HUS). STEC are
categorized into serogroups by their somatic O antigen. The STEC serogroup
most commonly identified and associated with severe illness and
hospitalization in the United States is E. coli O157; however, there
are over 50 other serogroups that can also cause illness. The majority of
infections are not reported to public health, because many individuals do not
seek health care or are not tested. In recent years, the number of clinical
laboratories that use tests that detect Shiga toxin or Shiga toxin genes has
increased, resulting in increased detection of both O157 and non-O157 STEC
infections.
Clinical Description
An infection of variable severity characterized by diarrhea (often bloody)
and/or abdominal cramps. Illness may be complicated by HUS (note that some
clinicians still use the term thrombotic thrombocytopenic purpura [TTP] for
adults with post-diarrheal HUS).
Laboratory Criteria
Confirmatory laboratory evidence
Isolation of E. coli O157:H7 from a clinical specimen,
OR
Isolation of E. coli from a clinical specimen with detection of
Shiga toxin or Shiga toxin genes.
Examples:
E. coli O157:H7 with or without Shiga toxin positive result (EIA
or PCR)
E. coli non-O157 (e.g. O121, O103:H2, etc.) & Shiga toxin
positive result (EIA or PCR)
Supportive laboratory evidence
Isolation of E. coli O157 from a clinical specimen without
confirmation of H antigen, detection of Shiga toxin, or detection of Shiga
toxin genes, OR
Identification of an elevated antibody titer against a known Shiga
toxin-producing serogroup of E. coli, OR
Detection of Shiga toxin or Shiga toxin genes in a clinical specimen
using a CIDT and no known isolation of Shigella from a clinical
specimen, OR
Detection of E. coli O157 or STEC/EHEC in a clinical specimen
using a CIDT.
Examples:
E. coli O157 & NO H antigen or Shiga toxin positive result
(EIA or PCR)
E. coli O157 Ab positive result (serology result usually performed
on a patient with HUS & NO positive STEC culture or Shiga toxin
result)
Shiga toxin positive result (EIA or PCR) only
E. coli O157 by PCR, EHEC by PCR, etc.
Epidemiologic Linkage
A clinically compatible illness in a person that is epidemiologically
linked to a confirmed or probable case with laboratory evidence,
OR
A clinically compatible illness in a person that is a member of a risk
group as defined by public health authorities during an outbreak.
Criteria to distinguish a new case of this disease or condition from
reports or notifications which should not be enumerated as a new case for
surveillance
A new case should be created when a positive laboratory result is
received more than 180 days after the most recent positive laboratory result
associated with a previously reported case in the same individual,
OR
When two or more different serogroups/serotypes are identified in one or
more specimens from the same individual, each serogroup/serotype should be
reported as a separate case.
Case Classification
Suspect
Identification of an elevated antibody titer against a known Shiga
toxin-producing serogroup of E. coli in a person with no known
clinical compatibility, OR
Detection of Shiga toxin or Shiga toxin genes in a clinical specimen
using a CIDT and no known isolation of Shigella from a clinical
specimen in a person with no known clinical compatibility, OR
Detection of E. coli O157 or STEC/EHEC in a clinical specimen
using a CIDT in a person with no known clinical compatibility, OR
A person with a diagnosis of post-diarrheal HUS/TTP (see
HUS case definition).
Probable
A person with isolation of E. coli O157 from a clinical specimen
without confirmation of H antigen, detection of Shiga toxin or detection of
Shiga toxin genes, OR
A clinically compatible illness in a person with identification of an
elevated antibody titer against a known Shiga toxin-producing serogroup of
E. coli, OR
A clinically compatible illness in a person with detection of Shiga toxin
or Shiga toxin genes in a clinical specimen using a CIDT and no known
isolation of Shigella from a clinical specimen, OR
A clinically compatible illness in a person with detection of
E.
coli
O157 or STEC/EHEC from a clinical specimen using a CIDT,
OR
A clinically compatible illness in a person that is epidemiologically
linked to a confirmed or probable case with laboratory evidence,
OR
A clinically compatible illness in a person that is a member of a risk
group as defined by public health authorities during an outbreak.
Confirmed
A person that meets the confirmatory laboratory criteria for
diagnosis.
For this disease/condition, Confirmed and Probable case statuses are
included in the released case count.
Comments
Asymptomatic infections and infections at sites other than the
gastrointestinal tract in people (1) meeting the confirmatory laboratory
criteria for diagnosis or (2) with isolation of E. coli O157 from a
clinical specimen without confirmation of H antigen, detection of Shiga toxin,
or detection of Shiga toxin genes, are considered STEC cases and should be
reported.
Although infections with Shiga toxin-producing organisms in the United
States are primarily caused by STEC, in recent years an increasing number are
due to infections by Shiga toxin-producing Shigella. Persons with (1)
detection of Shiga toxin or Shiga toxin genes using a CIDT and (2) isolation
of Shigella spp. from a clinical specimen should not be reported as an
STEC case.
Due to the variable sensitivities and specificities of CIDT methods and the
potential for degradation of Shiga toxin in a specimen during transit,
discordant results may occur between clinical and public health laboratories.
Persons with (1) detection of Shiga toxin or Shiga toxin genes using a CIDT
and (2) the absence of isolation of Shigella from a clinical specimen,
should be classified as a suspect or probable case, regardless of whether
detection of Shiga toxin or Shiga toxin genes is confirmed by a public health
laboratory.