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Published Date: 2011-04-29 11:12:44
Subject: PRO/AH/EDR> Salmonellosis, serotype Typhimurium - USA (02): laboratory acquired
Archive Number: 20110429.1331

SALMONELLOSIS, SEROTYPE TYPHIMURIUM - USA (02): LABORATORY-ACQUIRED
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Date: Thu 28 Apr 2011
Source: CDC, _Salmonella_ homepage [edited]
http://www.cdc.gov/salmonella/typhimurium-laboratory/042711/index.html

CDC is collaborating with public health officials in many states to
investigate a multistate outbreak of _Salmonella [enterica_ serotype]
Typhimurium infections associated with exposure to clinical and
teaching microbiology laboratories. Investigators are using DNA
analysis of bacteria obtained through diagnostic testing to identify
cases of illness that may be part of this outbreak.

As of 20 Apr 2011, a total of 73 individuals infected with the
outbreak strain of _S._ Typhimurium have been reported from 35 states:
AK (1), AL (3), AZ (2), CA (1), GA (5), IA (1), ID (2), IL (3), IN
(1), KS (1), KY (3), MA (2), MD (2), MI (2), MN (4), MO (2), NC (1),
ND (1), NE (2), NJ (2), NM (3), NV (1), NY (1), OH (1), OK (1), OR
(1), PA (6), SC (2), SD (1), TN (2), TX (1), UT (3), WA (5), WI (3),
WY (1).

Among persons with available information, illness onset dates range
from 20 Aug 2010 to 8 Mar 2011. Infected individuals range in age from
less than 1 year to 91 years old, and the median age is 24 years old.
63 percent of patients are female. 14 percent of patients have been
hospitalized. One death has been reported.

The numbers of new cases have declined substantially during the past
several months, and reports associated with this outbreak strain
appear to have returned to the expected baseline of approximately 0 to
4 cases reported per week.

Investigation of the outbreak
-----------------------------
In an epidemiologic study conducted during February and March 2011,
32 ill persons answered questions about exposures during the days
before becoming ill. Investigators compared their responses to those
of 64 persons of similar age previously reported to state health
departments with other illnesses (controls). Preliminary analysis of
this study has suggested exposure to clinical and teaching
microbiology laboratories is a possible source of illness. Illnesses
have been identified among students in microbiology teaching
laboratories and employees in clinical microbiology laboratories. Ill
persons (60 percent) were significantly more likely than control
persons (2 percent) to report exposure to a microbiology laboratory in
the week before the illness began. Additionally, multiple ill persons
reported working specifically with _Salmonella_ bacteria in
microbiology laboratories. The New Mexico Department of Health found
that the outbreak strain was indistinguishable from a commercially
available _S._ Typhimurium strain used in laboratory settings. This
commercially available strain was known to be present in several
teaching or clinical laboratories associated with ill students or
employees infected with the outbreak strain. These data suggest this
strain is the source of some of these illnesses. Additionally, several
children who live in households with a person who works or studies in
a microbiology laboratory have become ill with the outbreak strain.

As part of this ongoing investigation, CDC is working with state and
local health departments, the American Society for Microbiology, and
the Association of Public Health Laboratories to conduct a survey of
laboratory directors, managers, and faculty involved with clinical and
teaching microbiology laboratories to identify areas where
improvements in biosafety and laboratory safety training can be made
to prevent future illnesses.

Advice to students/employees in clinical and teaching microbiology
laboratories
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- Be aware that bacteria used in microbiology laboratories can make
you or others who live in your household sick, especially young
children, even if they have never visited the laboratory. It is
possible for bacteria to be brought into the home through contaminated
lab coats, pens, notebooks, and other items that are used in the
microbiology laboratory.

- Persons working with infectious agents, including _Salmonella_
bacteria, must be aware of potential hazards, and must be trained and
proficient in biosafety practices and techniques required for handling
such agents safely, including:

- Wash hands frequently while working in and immediately after
leaving the microbiology laboratory and follow proper hand washing
practices. This is especially important to do before preparing food or
baby bottles, before eating, and before contact with young children.

- Do not bring food, drinks, or personal items like car keys, cell
phones, and mp3 players into the laboratory. These items may become
contaminated if you touch them while working or if you place them on
work surfaces.

- Do not bring pens, notebooks, and other items used inside of the
microbiology laboratory into your home.

- Wear a lab coat or other protective uniform over personal clothing
when working in a microbiology laboratory; leave it in the laboratory
when you are finished. Remove protective clothing before leaving for
non-laboratory areas (such as, cafeteria, library, or administrative
offices). Dispose of protective clothing appropriately or deposit it
for laundering by the institution. Take it out of the laboratory only
to clean it.

- If you work with _Salmonella_ bacteria in a microbiology
laboratory, watch for symptoms of infection, such as diarrhea, fever,
and abdominal cramps. Call your health care provider if you or a
family member has any of these symptoms.

Advice to laboratory directors, managers, and faculty involved with
clinical and teaching microbiology laboratories
----------------------------------
- A comprehensive set of biosafety guidelines for work with
_Salmonella_ and other similar human pathogens can be found in the
Biosafety Level 2 section of the CDC/NIH Biosafety in Microbiological
and Biomedical Laboratories manual and the Guidelines for Biosafety
Laboratory Competency, MMWR Supplement
(http://www.cdc.gov/mmwr/preview/mmwrhtml/su6002a1.htm?s_cid=su6002a1_w).

- Non-pathogenic (attenuated) bacteria strains should be used when
possible, especially in teaching laboratories. This will help reduce
the risk of students and/or their family members becoming ill.

- Persons working with infectious agents, including _Salmonella_
bacteria, must be aware of potential hazards and trained and
proficient in the practices and techniques required for handling such
agents safely.

- Advise persons using the laboratory to watch for symptoms of
_Salmonella_ infection, such as diarrhea, fever, and abdominal cramps,
and to call their health care provider if they or a family member have
any of these symptoms.

- All students and employees using the laboratory should be trained
in biosafety practices.

- Ensure that handwashing sinks have soap and paper towels. Require
students and employees to wash their hands before leaving the
laboratory.

- Do not allow lab coats to leave the microbiology laboratory, except
to be cleaned.

- Do not allow food, drinks, or personal items like car keys, cell
phones, and MP3 players to be used while working in the laboratory or
placed on laboratory work surfaces.

- Place dedicated writing utensils, paper, and other supplies at each
laboratory station. These items should not be allowed to leave the
laboratory.

--
Communicated by:
ProMED-mail Rapporteur Brent Barrett

[Singh (Singh K: Laboratory-Acquired Infections. Clin Infect Dis
2009; 49: 142-7) has written a fine review on the subject of
infections acquired in the laboratory, which can be read at
http://cid.oxfordjournals.org/content/49/1/142.long. A whole host of
pathogens can be acquired in a laboratory representing viruses,
bacteria, mycobacteria, and fungi. The abstract is reproduced below:

"Laboratory-acquired infections due to a wide variety of bacteria,
viruses, fungi, and parasites have been described. Although the
precise risk of infection after an exposure remains poorly defined,
surveys of laboratory-acquired infections suggest that _Brucella_
species, _Shigella_ species, _Salmonella_ species, _Mycobacterium
tuberculosis_, and _Neisseria meningitidis_ are the most common
causes. Infections due to the bloodborne pathogens (hepatitis B virus,
hepatitis C virus, and human immunodeficiency virus) remain the most
common reported viral infections, whereas the dimorphic fungi are
responsible for the greatest number of fungal infections. Because of
the increasing attention on the role of the laboratory in bioterrorism
preparation, I discuss the risk of laboratory-acquired infection with
uncommon agents, such as _Francisella tularensis_ and _Bacillus
anthracis_. Physicians who care for a sick laboratory worker need to
consider the likelihood of an occupationally acquired infection while
advising exposed laboratory workers about postexposure prophylaxis. In
addition, physicians should be aware of the importance of alerting the
laboratory if infection with a high-risk agent is suspected."

The route of transmission to the laboratory worker can be enteric
(such as hand-to-mouth), transcutaneous (via a needle exposure) or
from an aerosol. Maintaining vigilance in the laboratory to prevent
transmission cannot be overemphasized. This is even more relevant with
diseases such as salmonellosis that can be secondarily spread in the
home as occurred in this report. - Mod.LL]

See Also