Download MRSA in companion animals: frequently asked questions

MRSA in companion animals: frequently asked questions
1. What is MRSA?
MRSA stands for methicillin resistant Staphylococcus aureus (although oxacillin is now used, the
terminology has stuck). Over 1400 distinct MRSA strains have been Identified in people, but most fall
into one of 11 clonal groups: five hospital acquired (HA) and six community acquired (CA). 96% of UK
human cases are associated with HA epidemic (E) clones E15 (27 subtypes) and E16 (23 subtypes). CAMRSA is less common but can be more virulent. CA-MRSA infections tend to be sporadic but human
patients frequently don't have any of the accepted risk factors for HA-MRSA infections (e.g.
immunocompromised, long-term hospitalised cases, patients with widespread skin and/or mucosal
defects, and surgical cases, especially those undergoing invasive procedures and/or those with
implants). MRSA infections are being increasingly reported in other species including dogs, cats, rabbits
and pet birds where the risk factors are similar. Resistance is also seen in other staphylococci,
particularly in the US. These include species important to small animals such as S. intermedius, S.
Schleiferi and some coagulase-negative staphylococci (CNS).
2. How common is MRSA?
Up to 30% of humans are colonised by Staphylococcus aureus but only a minority of these are
methicillin resistant strains (MRSA). Although some surveys reported that up to 40% of strains were
MRSA (giving an approximate carriage rate of 12%), most estimate that less than 1% of the general
population and up to 5-10% of healthcare workers carry MRSA. The 40% figure generally applies to cases
of S. aureus bacteriaemia, which are a lot less common than either colonisation and carriage or local
infections. Recent reports suggest that up to 10% of veterinary staff are colonised by MRSA.
The incidence in companion animals is largely unknown. Small scale, referral hospital based studies
suggest that up to 10% of dogs may carry MRSA and approximately 3% of recent submissions to
veterinary laboratories have involved MRSA, but these are obviously selected groups of animals. US
studies, in contrast have identified methicillin resistance in staphylococci from 15% of healthy cats and
38% of dogs with recurrent pyoderma, although these surveys were in an area with a high concentration
of healthcare premises and industries that may have biased the figures. There are ongoing large-scale,
epidemiological surveys to determine the prevalence in healthy dogs and cats in the UK and elsewhere
that will help answer this question.
3. Can MRSA pass from humans to animals, and from animals to humans?
Yes, although staphylococci are usually adapted to their preferred hosts. S. aureus is mostly isolated
from humans and horses (although these appear to be different strains), whereas dogs are
predominantly colonised by S. intermedius, and cats by S. intermedius and S. felis. Methicillin resistant
strains of S. intermedius and other species carried by domestic animals have also been recognised.
Staphylococci can, however, opportunistically cross species barriers under some circumstances. Virtually
all small animal isolates in the UK have been HA-MRSA E15 and E16, implying that the organisms
originated from humans. In recent studies, 45% of owners of dogs with deep pyoderma were colonised
with the same strain of S. intermedius (NB these were not methicillin resistant) and 16/88 humans (plus
one cat) in contact with eight canine MRSA cases were colonized. MRSA has also been isolated from up
to 17% of veterinary staff and 11% of owners in-contact with infected animals. In a Canadian study,
concurrent human-animal colonisation was found in 20% of households with S. aureus positive humans
and 67% of S. intermedius positive humans.
It is important to differentiate colonisation from infection in this context. Simple colonisation presents
very little risk to healthy humans, but people who are immunocompromised, have open wounds or
implants etc. may be more vulnerable. Acquisition of MRSA infections from animals remains sporadic
and rare, and associated with the above risk factors. Animals may also act a reservoir for re-infection in
MRSA endemic households, although they were probably colonised from the owners in the first place. It
is therefore important to consider pets in any household eradication policy.
4. Are MRSA infections in animals increasing?
On the face of it, yes, but studies on methicillin resistant infections in animals are in their infancy.
Preliminary, referral hospital based studies suggest carriage in 10% of dogs. MRSA comprise
approximately 3% of submissions to veterinary laboratories. Recognition of the problem, better isolation
techniques and better reporting may all have contributed to the apparent increase in cases. Better data
will allow more accurate monitoring of trends in the future. Despite this, infections remain uncommon.
5. Can my bird get MRSA?
Yes birds too can get MRSA infections. They have been reported in chickens and have also been
identified in pet psittacines in association with chronic ulcerative dermatitis and pyoderma.
6. Is MRSA a risk to my staff and clients?
Not under most circumstances (see also FAQ 3 above). Colonisation is not uncommon and is of little
significance in healthy humans. Adherence to routine hygienic precautions, particularly hand washing,
will prevent colonisation in most circumstances. People who are, however, immunocompromised, have
implants or skin and/or mucosal barrier defects are at greater risk of colonisation and infection, and
should take greater care.
7. Should my practice implement an infectious disease control policy?
Yes; this is important to monitor and control not only MRSA but other potential problems such as
methicillin sensitive staphylococci, Pseudomonas. Salmonella etc. MRSA can be directly disseminated for
up to 2-4m by exfoliation and droplet spread from human patients, and beyond by poor hygiene
measures. MRSA and other species will readily contaminate suitable microhabitats found throughout
veterinary and medical premises.
Guidelines available from BSAVA can be adapted to suit individual practices. Any infectious disease
control policy should address: policies for identification and management of MRSA cases, measures to
prevent the spread of MRSA and infectious organisms (including cleaning, hand washing, and the
rational use of appropriate antibacterials and disinfectants), infectious disease control audits and
strategies for routine sampling of the premises and/or staff (see FAQs 7 and 8).
8. Should we routinely monitor for MRSA?
This is a very controversial area. Several laboratories have been inviting practices to adopt surveillance
schemes, but it is unclear how effective these are in both determining and managing the risk of MRSA.
Post-infection cultures cannot be used to determine how the infection occurred with any reliability.
Many culture methods are qualitative rather than quantitative and as it is unfeasible to have any
completely sterile practice environment, you are almost certainly guaranteed to find something. No
figures, furthermore, for acceptable microbiological levels in medical or veterinary premises have been
established. If surveillance is used, it is essential that it is conducted following advice, is done with a
reputable laboratory (an MRSA working group is currently establishing best practice guidelines for
culture and identification) and that the policy has clear aims.
9. Should we routinely swab our premises for MRSA?
Given the caveats above, the extent and frequency of environmental sampling depends on the
individual situation and circumstances. MRSA can survive up to 12 months in hospital dust, bedding and
clothing. Routine environmental screening could therefore be used to monitor cleanliness - one study
showed that of 82-91% of visually clean surfaces only 30-45% were microbiologically clean. MRSA
contamination rates have declined where cleaners have been trained to think about microbiological
cleanliness. There are few studies of MRSA contamination in veterinary premises. One in Canada
isolated MRSA from 10% of samples (tables 4%; floors 3%; telephones, key¬boards and taps 2%;
kennels, stethoscopes and otoscopes 1%).
Environmental monitoring is probably of most use when investigating the epidemiology of a series of
infections and/or to monitor the effectiveness of infection control strategies. Sites could include
operating and examination tables, anaesthetic machines, floors, walls and fittings, cages, and
equipment, but hand-touch sites and clinical equipment seem to be most important in transmission.
Contaminated sites should be thoroughly cleaned and disinfected with an effective product.
10. Should we routinely swab our staff for MRSA?
Surveillance of staff is highly controversial and issues of consent, confidentiality, stigmatisation and
further action must be addressed. Screening can also miss transiently contaminated staff, who may still
act as a source of infection if they fail to observe adequate hygienic precautions. Colonised staff that are
scrupulous about hygiene may actually be of less concern. Screening should therefore be done to
identify problems in infectious disease control, and not to apportion blame or as a substitute for control
measures.
It is important to differentiate transient carriage from colonisation and persistent carriage Transient
carriage is more common and is most effectively controlled by hygiene measures. Generally, isolation of
MRSA in the morning or away from work indicates colonisation, whereas isolation only during or soon
after work indicates transient contamination. The number of screening cultures is controversial, but
three swabs 5-7 days apart and at different times are usually taken. MRSA-positive staff or owners of
MRSA-positive animals that wish to be tested should be referred to their doctor for further investigation
and treatment.
Screening may help if MRSA becomes an endemic problem and/or the epidemiology of the infections
suggests contact with particular staff members. It is difficult, however, to prove that an infection was
acquired in the practice in the absence of pre-admission culture, as asymptomatic and/or transient
carriage is not uncommon and is not necessarily relevant. Any resident animals (e.g. the practice cat)
should also be screened.
Any MRSA-positive staff, or owners of MRSA-positive animals that wish to be tested, should be referred
to their doctor for advice on treatment and any further action.
11. When should I suspect MRSA?
Methicillin resistant staphylococci tend to be associated with opportunistic and wound infections, with
fewer skin, ear and other infections compared to methicillin-sensitive species. MR S. aureus and S.
schleiferi tend to be involved with more serious deeper infections that MR S. intermedius. Screening all
cases prior to admission is not feasible, especially in first opinion clinics. The prevalence and risk factors
for carriage MRSA in healthy dogs and cats is as yet unknown and some asymptomatic carrier animals
will be undetected. At present, MRSA should be suspected in:
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Patients from known MRSA positive households or that belong to healthcare workers.
Patients with non-healing wounds.
Patients with non-antibiotic responsive infections where previous cytology and/or culture
indicates that staphylococci are involved.
Nosocomial or secondary infections, especially in at-risk patients.
Screening hospitalised cases during their stay and/or prior to discharge may be necessary in an
environment where MRSA is endemic and/or there is evidence of transmission in the practice.
12. What should I do if I suspect MRSA?
The two most important steps are culture and communication. Staff should be informed about sus¬pect
MRSA cases before admission, although this may not be possible in first opinion practice. Practices,
however, should culture suspected cases before referral. If in doubt, take a swab at admission and
proceed as though MRSA positive until you have the results. This might involve cultures of skin lesions or
wounds, surgical sites, implants or drains, insertion sites of intravenous catheters, joint fluid, urine,
faeces, and sputum or bronchiolar lavage fluid etc. Nasal swabs detect approximately 75% of human
naso-pharyngeal (i.e. mucosal) carriers. Including throat and perineal swabs increases the detection rate
to 98%. Swabs should be submitted in transport medium to a laboratory capable of isolating MRSA and
accurately reporting antibiotic sensitivity. MRSA con¬trol measures should be implemented whilst
awaiting the bacteriology results.
13. I have identified MRSA in a case. What should I do?
MRSA is treatable, but treatment can be complicated by resistance to a range of antibiotics. De¬spite
this, MRSA are often sensitive to antibiotics that are commonly used in veterinary practice and most
animals with MRSA will survive. Death is attributable to the underlying condition and not the MRSA in
approximately 50% of fatal cases.
The microbiology laboratory that isolated the MRSA will report the antibiotic sensitivity pattern and
advise you on treatment. You may also want to get advice on the primary condition and the spe¬cific
problem that the MRSA is causing, e.g. from a dermatologist for skin problems, an orthopae¬dic surgeon
for stifle infections, a soft-tissue surgeon for wound infections, an internist for catheter infections etc.
Treatment is based on the individual case but will usually involve managing the MRSA infection, the
primary condition and any other predisposing factors.
The animal can be discharged once the infection and primary clinical problem have resolved. You may,
however, want to screen the animal for persistent MRSA carriage and discuss further antibi¬otic
treatment or hygienic precautions with the owner as appropriate. It is unfeasible to screen every inpatient prior to discharge, and it is possible some animals that become persistent carriers during
hospitalisation will be undetected. Pre-discharge screening, however, is only a measure of the
colonisation rate in the practice and it is uncertain whether this is of much clinical importance in healthy
individuals. Preliminary data suggest that most animals with MRSA infections have mucosal colonisation,
although it is unclear whether this is a cause or consequence of infection. If the animal remains
colonised potential risks and precautions must be discussed with the owner.
14. Is decolonisation feasible?
Decolonisation can be attempted in persistently colonised animals. Decolonisation of humans of¬ten
involves 3-5 days intranasal fucidin or mupirocin and chlorhexidine washes, and then three negative
screens 2-5 days apart, with repeated cycles if necessary. Treatment results in clearance in 91-99% of
patients but re-colonisation rates are up to 26%. Recent reports suggest that suc¬cessful decolonisation
in dogs requires much longer courses of treatment; 2-3 weeks can be re¬quired in some cases.
Treatment options include antibacterial shampoos and 2% fusidate/fusidic acid (Fucithalmic®; Fucidin®
(NB not licensed for animals) or 2% mupirocin (Bactroban® Nasal; NB not licensed for animals)
intranasally 2-3 times daily. Other antibiotics may be appropriate de¬pending on the sensitivity pattern.
There are also concerns about the risks of inducing resistance to these drugs - Scandinavian countries
have banned the use of mupirocin in animals, and the Health Protection Agency and Department of
Health have expressed concern over the use of fusidate in the UK. At present, non-antibiotic
decolonisation methods are preferred, and it is recom¬mended that antibiotic-based decolonisation
attempts are used as a last resort and only where in¬dicated (e.g. in particularly high-risk situations).
The practicalities of administering any of the treatments in any species should be considered at the
outset as partial or incomplete administra¬tions could also lead to further resistance.
15. Where did the infection come from?
This is a difficult question to answer. In the absence of a pre-admission screen, it is impossible to
determine whether the infection was acquired in the practice environment or whether the animal was
already colonised before admission. Most dogs and cats are infected with the same strains that affect
humans and it is assumed that humans are the principle reservoir. Animals can, how¬ever, become
persistently or transiently colonised and act as a source of infection for in-contact humans and animals.
MRSA can also be transmitted by mechanical carriage on hands, hair, clothes and bedding, surfaces,
equipment and other fomites.
The complicated nature of the epidemiology is illustrated by the following schematic diagram:
Solid line - likely route of transmission/contamination
Broken line- less likely route of transmission/contamination
16. What about animals that visit healthcare premises?
Animals that routinely visit healthcare institutions include dogs and cats taken into old people's homes,
hospices, hospital wards and children's wards etc. There is no doubt that these can be benefit mental
wellbeing and recovery from illness. There is the possibility, however, that these animals could be
carriers of MRSA or other zoonoses, or act as mechanical vectors for transmis¬sion between patients
and staff. The risk of this compared to the risk from other patients, staff and visitors should, however, be
kept in proportion. It is impractical to suggest that animals are bathed or otherwise treated between
patients, but steps that could be taken to minimise any risk include:
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Ensuring that the animals are clinically healthy, vaccinated, and on thorough endo- and ectoparasite control programmes, preferably under the supervision of a veterinary surgeon.
Screening for dermatophytes in the absence of clinical lesions is not practical; Wood's lamps
have low sensitivity and specificity, and fungal culture may simply represent transient
contamination from the environment. Empirical systemic or topical antibiotic therapy is not
recommended because of the likelihood of rapid re-colonisation and the development of
antibiotic resistant strains of bacteria.
Grooming to remove loose hairs and scale, and, where possible, bathing with an effective
antibacterial shampoo prior to visiting.
Preventing access to sites and/or patients known to be colonised or contaminated by MRSA,
critical care, immunosuppressed and other high-risk patients such as those with implants and
epidermal or mucosal barrier defects.
Staff and patients should wash their hands with an effective disinfectant immediately after
handling an animal. The floor and other hard surfaces that the animals come into contact with
should also be disinfected.
Licking and other forms of mucosal contact should be avoided.
Animals should not climb on beds or other furniture. Where this is necessary (e.g. with cats and
other small animals or bedridden patients) an impermeable pad (e.g. incontinence pad) should
be placed under the animal. If contamination is suspected the surface should be disinfected or
the bedding changed as appropriate.
Animals should not be present when patients are eating, during cleaning and changes of
bedding and when any medical or surgical procedures are undertaken.
Routine screening of animals would be expensive, time-consuming and all the above caveats
about transient contamination versus colonisation also apply. Visiting or resident animals should
be included with other regular (i.e. human) visitors, staff and patients if culture and monitoring
of MRSA is undertaken however. A study in Canada, furthermore, did not isolate MRSA from
dogs that visited hospitals.
17. What should I do if I suspect MRSA infection, but the owner will not pay for testing?
There are no provisions for free MRSA testing in animals and birds. The responsibility lies with the owner
and, in case of the environmental testing, with the practice itself.
18. What is PVL?
PVL stands for Panton Valentine Leucocidin. This is an extremely potent toxin that has been associated
with severe skin infections and, occasionally, a rapidly fatal septicaemia. PVL producing strains of S.
aureus can affect healthy individuals, for example the young Royal Marine who contracted the infection
during training. Fortunately, PVL infections are extremely rare in the UK. Up to 1.6% of S. aureus isolates
have the PVL gene, but these represent a diverse range of methicillin resistant and sensitive clones,
mostly from community acquired rather than hospital acquired strains. No isolates from animals in UK
have been found to carry the PVL gene so far. In contrast, up to 50% of MRSA isolates from animals in
the US carry the PVL gene, although no methicillin resistant S. schleferi isolates (an important
pathogenic species for dogs in the US) were found to do so. Possession of the PVL gene, however, does
not imply that the PVL toxin will be clinically important and there are no reports of PVL-associated
infections in animals.