Spread of veterinary MRSA in The Netherlands

Traditionally, meticillin resistant Staphylococcus aureus (MRSA) has been
considered as a hospital associated pathogen. Since approximately 10 years,
MRSA has expanded its territory to the community causing severe infections in
previously healthy persons all over the world. In 2005 a new clone of MRSA was
observed in The Netherlands that is related to an extensive reservoir in pigs
and cattle (V-MRSA). A survey among pigs at slaughterhouses showed that 40% of
all pigs were colonized with MRSA. By the end of 2007, approximately 30% of all
new MRSA strains in The Netherlands were V-MRSA.
Individuals who are living on animal farms but not in direct contact with
animals had a lower carriage rate (approximately 2%). A recent survey among
meat in retail showed that nearly 10% harbored V-MRSA. V-MRSA may spread into
the population from direct or indirect contact with animal farms or from
handling or consuming contaminated meat. The first transmission route is
considered most likely and will occur first in areas with a high density of pig
farms. The second route (meat) is considered less likely but may have much
larger impact.
The prevalence of MRSA in the general population of The Netherlands was in 2007
still very low (<0.5%). If V-MRSA can successfully spread from human to human
outside the known high risk group into the population it will constitute a
significant public health problem in the near future. This will necessitate
major adaptations of the existing guidelines for control in the community and
in healthcare institutions. It is questionable if the current control strategy
in The Netherlands can be maintained in this scenario. At least the associated
costs will increase significantly. The public health impact of V-MRSA will
depend mainly from its ability to spread in the population outside animal
farms.

The primary objective of this study is to determine the prevalence of V-MRSA in
areas with high density of pig farming compared to the expected prevalence of
MRSA in the general population of The Netherlands and as a secondary objective
to assess the amount of spread of V-MRSA into the population of The
Netherlands.

1500 randomly chosen individuals will be sent a short questionnaire, a patient
information letter and informed consent by mail. Participation of subjects is
voluntary and based on informed consent. Subjects are also asked to approve a
sampling and that they can be contacted afterwards for an extensive
questionnaire. After the written informed consent is obtained, participants
will subsequently be sent a nasal swab which can be returned by mail in the
appropriated packaging. The swabs will be sent and cultured for the presence of
MRSA at the several laboratories. A total of approximately 600 samples will be
included in the study initially. Furthermore, Multi-locus variable-number
tandem-repeat analysis (MLVA) and the spa typing of the V-MRSA strains will be
performed at the RIVM. When MRSA prevalence of 2% or more is found the study
will be continued by phase two.
In the second phase a nested case-control study will be performed based on the
first survey to identify determinants for
V-MRSA carriage in relation to animal farms and handling and/or consuming meat.
Individuals who are colonized with
V-MRSA are compared with individuals who are not colonized with V-MRSA strains.
In addition, subjects with HA-MRSA will be excluded. All selected subjects will
be sent a questionnaire. At least the following variables will be included in
the questionnaire: Age, gender, contact with animals (which kind and how
often), presence of animals in the house, preparation and/or consumption of
meat (which kind and how often), antibiotic use in the last six months,
underlying disorders (e.g., eczema, psoriasis or other skin diseases, lung
diseases (COPD), allergy, recurrent upper respiratory tract infections,
malignancies, immunosuppressive drugs, foreign bodies, history of recurrent
furunculosis), history of MRSA infection and/or colonization, profession, being
active in a contact sport, household member working on an animal farm and
presence of indwelling catheters and/or open wounds.
If the results of phase one indicate spread of V-MRSA into the community a
similar survey is performed in several communities with an extremely low
density of animal farms. This survey is mainly focused on the potential spread
from contaminated meat.

Participation in the study does not take much time and there are no invasive
procedures. Altogether, only one nose swab sample will be taken and will be
sent to one of the collaborated laboratories for identification of MRSA. Taking
nose swab should not be considered to be much discomfort to the subjects.
Furthermore, two questionnaires will be taken to identify determinants for MRSA
carriage in relation with direct animal contact and consumption and/or
preparation of contaminated meat. There will be no physical or physiological
discomfort, no site visits and no physical examinations or other tests
associated with participation. Therefore, participation in the study will not
involve any substantial risk for the included subjects and the investigators
will not interfere with treatment.