Infections acquired in clinical environments are known as Hospital Acquired Infections or HAI; Risk is increased when very sick animals require more intensive treatment; Many HAI-causing bacteria are resistant to antibiotics; The single most important way to reduce HAIs is improved hygiene practices for healthcare workers; MRSA appears in dogs and cats usually as wound infections, urinary tract infections, pneumonia, sepsis and endocarditis; It is thought that humans are the most likely source of veterinary infections; It is unlikely that HAIs will ever be eradicated.

Infections acquired in clinical areas (usually called Hospital Acquired Infections or HAIs) have been a major problem in human healthcare for many years. Generally, they are found most often to affect patients in Intensive Care, and it is strongly suspected that there is a similar associated risk in veterinary medicine. In particular, risk of infection is more likely when extremely sick animals require more intensive treatment and use of devices such as urinary and intravenous catheters, longer hospitalisation or intensive care practices and use of antimicrobial and immunosuppressive drugs. It is unknown what the incidence of HAI in veterinary medicine is, but it certainly appears to be increasing.

Common human HAIs include blood stream infections (septicaemia), urinary tract infections, surgical wound infections, infectious diarrhoea and pneumonia and are seen also in the veterinary field with the addition of joint infections and occasionally body cavity infections. Pneumonia seems to occur less frequently compared to humans, probably because few veterinary patients undergo long-term ventilation.

Many of the bacteria that cause HAI are resistant to a range of antibiotics and include Meticillin-resistant Staphylococcus aureus (MRSA), multi drug-resistant E. coli and Vancomycin-resistant enterococcus. Although Pseudomonas can also be a problem it is inherently resistance to many antibiotics and has been known to be a problem for much longer. These infections are difficult and expensive to treat and are likely to be a risk to veterinary staff attending infected patients as well as to other patients.

The best measures for controlling HAIs have been a cause of great debate. The approach taken in some countries (e.g. the Netherlands) where MRSA rates in human hospitals have been kept to a minimum by aggressive screening of all healthcare staff and patients is impractical in the UK where MRSA is thought to be endemic in hospitals. Here, despite huge amounts of money spent on reducing the incidence of HAIs, the approaches that seem best are simple and inexpensive to implement. The most important intervention is improving the hygiene practices of health care workers. In veterinary medicine we have always been aware of biosecurity, but until recently there has been little focus on general clinic and personal hygiene for routine cases because these were considered non-infectious. However, a change in the profession’s awareness of veterinary hospital acquired infections and how they can be minimised has been prompted by public and professional concerns.

Meticillin was first used in 1959 because staphylococcus aureus was becoming resistant to antibiotics such as penicillin. The first clinical case of MRSA infection was reported in 1961. and nowadays we recognise that MRSA generally shows resistance to a range of antibiotics rather than just Meticillin (which is now rarely used) thus making it very hard to treat.

MRSA in veterinary medicine is currently the most high profile HAI although not the most deadly. It has been known to cause disease in human patients since the early 1960s and is known to cause a large number of different infections in people including post-operative wound infections, infection of implants, catheter infections, endocarditis and sepsis although in healthy people the bacteria generally causes no problems.

The common staphylococcus in dogs is S. intermedius rather than S. aureus, and although MRSA infection has been reported in the veterinary literature since 1999, it was not considered to be a major concern until recently. Over the last three years however there have been increasing reports of MRSA infections both from the bigger UK veterinary hospitals and from the veterinary clinical microbiology laboratories. Reports have also been made of MRSA infections in horses in North America, one of which showed that the bacteria infecting the horses was found to be identical to the bacteria colonising some of the equine staff. There has also been at least one reported case of a pet being the source of recurrent MRSA infections in an owner.

There is relatively little published in the veterinary so far, but experience suggests that MRSA may cause infection in both dogs and cats where a wide variety of infections have been identified. These include wound infections (both chronic non-healing wounds and post-operative wounds), urinary tract infections, pneumonia, sepsis and endocarditis. Specific veterinary risk factors for MRSA have not been identified; however it is probable that they are similar to those found in people and likely to cause more of a problem as veterinary medicine advances and increasingly sick patients are treated.

Anecdotally, the majority of veterinary patients with MRSA have had localised infections which have been successfully treated. However, the disease can be fatal if the patient develops MRSA sepsis. Most recently, strains of MRSA that produce the tissue toxin Panton-Valentine leucocidin (PVL)) have been found in dogs in the USA and Netherlands. The PVL toxin has been shown to be responsible for some of the more severe effects of infection such as furunculosis, severe necrotising pneumonia and necrotic lesions of the skin and soft tissues.

It is well known in human medicine that the hands of health care workers represent the main mode of transmission of MRSA between patients, and that the main source of MRSA being other infected or colonised patients or health care workers. Although the precise current UK colonisation rate for the general public is not known, it is generally thought to be in the region of 3%. Worryingly, several studies have suggested that the colonisation rate of veterinary staff is in the range of 10-20% – significantly higher than that thought to occur in the general public. Because of this it is highly unlikely that we can prevent MRSA entering our veterinary hospitals and practices.

The colonisation rate of animals is not known. Although S. intermedius is the main staphylococcus of dogs, they can become colonised by S. aureus, and a small-scale study in the Queen Mother Hospital at the Royal Veterinary College suggested that a proportion of dogs (up to 10%) may be colonised on admission. It possible that dogs and cats can be a source for their own infection, but it is probably equally likely that veterinary staff or other personnel working with sick pets may also act as the source.

The presence of MRSA in the environment may also play a role in infection. The people working there can transfer bacteria from environmental surfaces to patients, and several studies have found that MRSA can survive in conditions similar to those found in the hospital environment for long periods of time. Thorough cleaning of the environment is an essential means of controlling or preventing outbreaks of MRSA.

Airborne transmission is thought to be much less important although it may still occur. MRSA usually colonises the nose, and thus it is possible for bacteria to be exhaled with the breath. For that reason the wearing of masks is important during clinical procedures that invade the skin. It is also possible, though less likely, that healthcare workers can become colonised by inhaling MRSA and then transmit the infection to patients.

It seems likely that humans are the source of most veterinary infections. In most Western countries (including the UK and USA), MRSA infection rates have reached the level where a search and destroy policy as implemented in the Netherlands is no longer possible and attention has concentrated on measures to reduce transmission. A strict hand washing policy is the single most important measure that can reduce the risk of infection occurring. Although this may seem straightforward, it is well-known from research that compliance by nurses and doctors is poor both in frequency and technique. Hands should be washed thoroughly before and after handling every patient even if gloves are also worn. Alcohol based handrubs can also be used and in a busy environment may improve compliance.

The age of relying on ever more powerful antibiotics is probably drawing to a close. If superbugs are to be overcome, utilisation of multiple control strategies based on an understanding of epidemiology and transmission is essential. Unfortunately it is extremely unlikely that HAIs will ever be eradicated, particularly with the ever-increasing advances in diagnostic and therapeutic techniques that are now being delivered in veterinary medicine. A proactive approach to HAIs will help to reduce their frequency and improve the relationship between pet owner and vet.