FROM THE BENCH
The Recovery of Nontyphoidal Salmonella from
CIDT-positive Stool Specimens
By Katie Dillon, ORISE Research Fellow, Enteric Diseases Laboratory Branch, CDC Division of Foodborne, Waterborne and Environmental Diseases
The Challenge
Salmonellosis continues to be
an important foodborne illness;
nontyphoidal Salmonella is the number
one cause of bacterial foodborne illnesses,
hospitalizations, and deaths in the United
States. 1 The Centers for Disease Control
and Prevention (CDC) estimates that
Salmonella causes 42,363 illnesses, 19,533
hospitalizations, and 378 deaths each
year. 1 Given the public health burden
that Salmonella imposes, fast, accurate
diagnostic tests are needed.
Recently, culture-independent diagnostic
tests (CIDTs) have emerged as an
alternative to culture-based methods and
are proving to be faster, cheaper and more
sensitive than culture-based methods. 2 In
general, CIDTs offer advantages such as:
• Quick turnaround time, allowing care
providers to determine the cause of an
enteric infection or intoxication
• Potentially increased sensitivity and
reduced costs compared to classic
culture-based methods
• Increased ease of use. 3
While CIDTs offer advantages to
healthcare workers and patients, they
also pose important challenges to public
health. Public health laboratories (PHLs)
and public health surveillance networks
like PulseNet rely on isolates recovered
using culture-based methods. These
isolates are used for characterization,
antimicrobial resistance testing and,
most recently, subtyping using whole-
genome sequencing (WGS). 3 Since clinical
laboratories do not need to generate a
culture isolate to perform a CIDT, the
burden of isolation is shifting to PHLs
to maintain the integrity of surveillance
systems. 4
The goal of the Salmonella Isolate
Recovery Project is to provide optimized
recommendations for efficient recovery
of Salmonella from CIDT-positive stool
specimens to maintain Salmonella isolate
availability, minimize costs, and improve
turnaround time, ultimately lessening the
current burden on PHLs.
How We Did It
Initially, we reviewed the current methods
with which PHLs were isolating Salmonella
from CIDT-positive stool specimens and
used that data to select the variables that
would be evaluated to determine the
optimized workflow. Since there were
many conditions to test, the laboratory
work was divided into three phases. In
the first phase, we tested two storage
temperatures for specimens prior to
testing, two transport media, and two
plating media to determine the effect each
condition had on the ability to recover
Salmonella from stool. In the second phase,
we tested five transport temperatures to
address isolate recovery from specimens
that are transported under warm and hot
Additional Authors:
Enteric Diseases Laboratory Branch, CDC
Division of Foodborne, Waterborne, and
Environmental Diseases:
• John Besser, PhD
• Heather Carleton, MPH, PhD
• Andrew Huang, PhD
• Jasmine Hensley, ORISE Research Fellow
• Eija Trees, PhD, DVM, APHL Contractor
• Amanda (Jo) Williams-Newkirk, PhD
Office of the Director, CDC Division
of Foodborne, Waterborne, and
Environmental Diseases:
• Anna Blackstock, PhD
The findings and conclusions in this report are
those of the author(s) and do not necessarily
represent the official position of CDC.
Salmonella on selective plating media. Photo: CDC
26
LAB MATTERS Fall 2019
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