| Adam Hart 2008-01-29, 3:25 am |
| Dispatch
http://www.cdc.gov/ncidod/EID/vol11no12/05-0428.htm
Methicillin-resistant Staphylococcus aureus in Pig Farming
Andreas Voss,*† Frans Loeffen,* Judith Bakker,* Corne Klaassen,† and
Mireille Wulf*
*Radboud university Medical Centre, Nijmegen, the Netherlands; and
†Canisius-Wilhelmina Hospital, Nijmegen, the Netherlands
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We conducted a study among a group of 26 regional pig farmers to
determine the methicillin-resistant Staphylococcus aureus prevalence
rate and found it was >760 times greater than the rate of patients
admitted to Dutch hospitals. While spa-type t108 is apparently a more
widespread clone among pig farmers and their environment, we did find
other spa-types.
Methicillin-resistant Staphylococcus aureus (MRSA) has become a major
nosocomial pathogen, highly prevalent in many European countries and
throughout the world (1). In the Netherlands, the prevalence of MRSA
among clinical isolates is still <1%, among the lowest in Europe (1).
This low prevalence is probably best explained by the national policy
that entails strict screening and isolation of all persons who are
considered at high risk for MRSA when admitted to a hospital. This
high-risk population has essentially consisted of patients admitted to
or treated in foreign hospitals. As a result of this policy for all
healthcare institutions, the prevalence of MRSA in the Dutch community
is extremely low as well. In a recent study among ˜10,000 patients
admitted to 4 Dutch hospitals, 23% carried S. aureus, but only 0.03%
of the isolates were methicillin-resistant (2).
In July 2004, we unexpectedly found MRSA in the preoperative screening
cultures of a 6-month-old girl before thoracic surgery. Neither the
girl nor her family (parents, 1 sister) had a history of traveling or
admission to a foreign hospital. In the following months, the girl
remained colonized with MRSA during consecutive decolonization
attempts. Subsequently, the girl's parents were found to be positive
for MRSA. The family lived on a farm and raised pigs.
To further investigate pig farming as a possible source of MRSA in
Dutch patients, we screened a selection of pigs owned by the
MRSA-positive farmer, and other regional pig farmers in November 2004.
In January and February 2005, 2 new cases of MRSA were identified, one
in a pig farmer from a different region and one in the son of a
veterinarian who worked mostly with pigs. Subsequently, the strain was
also isolated from the veterinarian and from a nurse in the hospital
unit to which the son was admitted.
Although the aforementioned cases were unrelated in time and location,
they shared some features. In all the cases, other family members were
MRSA-positive, decolonization was repeatedly unsuccessful, and
genotyping performed in the National Institute of Public Health and
Environment (RIVM, Bilthoven, the Netherlands) showed the strains were
not typeable by pulsed-field gel electrophoresis (PFGE) with
restriction endonuclease SmaI (the standard method).
The Study
Initially, the nares of 10 pigs were cultured. All were negative for
MRSA. At a later stage, the perineum of 30 pigs was cultured; 1 was
positive for MRSA. The regional pig farmers were screened (throat and
nares) during a monthly professional meeting that happened to be on
the farm of the MRSA-positive family, at the time of investigation.
With the exception of this meeting, the farmers had no further
epidemiologic links, other than being from the southeastern region of
the Netherlands. Six (23%) of the 26 farmers were colonized with MRSA.
As mentioned above, all MRSA isolates were resistant to digestion with
restriction-endonuclease SmaI, when typing with PFGE was attempted. To
ensure that we did not falsely classify a pig-related staphylococcal
species as MRSA, the identification of all isolates was confirmed by
testing for the presence of a S. aureus–specific DNA element as well
as the MecA gene, according to the methods of Reischl et al. (3). To
compare the MRSA isolates, we performed random amplified polymorphic
DNA analysis with primers Eric II (5´-AAG TAA GTG ACT GGG GTG AGC
G-3´), RW3A (5´-TCG CTC AAA ACA ACG ACA CC-3´), D14307 (5´-GGT TGG GTG
AGA ATT GCA CG-3´) and spa-typing.
Overall, 3 different MRSA strains were identified. The isolates of the
girl (case-patient A), her parents, and the pig from their farm were
identical with random amplified polymorphic DNA and belonged to
spa-type t108. Furthermore, one of the regional pig farmers screened
during the meeting, the pig farmer from a different region
(case-patient B), the young boy (case-patient C), as well as his
father and the nurse who treated the boy, were colonized with the same
strain (Table). Three of the regional pig farmers shared spa-type 567.
The isolate from the remaining MRSA-positive regional farmer showed a
spa-type not previously described (Table).
Conclusions
Recently, MRSA has been found in horses and in persons who take care
of them (4). Human carriage has also been linked to colonized
companion cats and dogs (5,6). While Lee et al. (7) reported an MRSA
isolation frequency of 0.6% in major food animals, but did not find
MRSA in 469 samples from pigs, Armand-Lefevre et al. (8) described S.
aureus (methicillin-susceptible and -resistant) carriage among pigs
and pig farmers. Although the authors showed that both farmers and
pigs carried methicillin-sensitive S. aureus and MRSA and that both
groups shared certain multilocus sequence typing, the isolates came
from separate, nonrelated collections.
Here we demonstrate transmission of MRSA between an animal and human
(pig and pig farmer), between family members (pig farmers and their
families), and between a nurse and patient in the hospital. The
unexpected high frequency of MRSA among the group of regional pig
farmers (>760× higher than in the general Dutch population) indicates
that their profession might put them at risk for MRSA colonization.
Overall, we found 3 different MRSA strains, including a new spa-type.
Therefore, we expect that multiple strains are present in the pig
population and the pig farmers. The strain with spa-type t108 appears
to be more prevalent and widespread, given that the strain spread from
animal to human, between family members, between patient and nurse,
and among pig farmers from different regions.
Further research on a larger scale is needed to see if these
observations hold true in other regions. If so, pig farming poses a
significant risk factor for MRSA carriage in humans that warrants
screening wherever pig farmers or their family members are admitted to
a hospital.
Dr Voss is a consultant microbiologist and head of infection control
at the Canisius-Wilhelmina Hospital and professor of infection control
at the Radboud university Medical Centre. His primary research
interests are nosocomial infections, including multidrug-resistant
nosocomial pathogens such as MRSA.
References
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Suggested citation for this article:
Voss A, Loeffen F, Bakker J, Klaassen C, Wulf M. Methicillin-resistant
Staphylococcus aureus in pig farming. Emerg Infect Dis [serial on the
Internet]. 2005 Dec [date cited]. Available from
http://www.cdc.gov/ncidod/EID/vol11no12/05-0428.htm
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