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Hospital-associated infections

ISSN 2398-2950

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Synonym(s): Hposital-acquired infections; Nosocomial infections


  • Hospital-associated, or nosocomial, infections are infections that occur in response to hospitalization.
  • Hospital-associated infections (HAIs) may be endogenous or exogenous.
  • They may develop from the endogenous flora of the patients or from exogenous microorganisms acquired from the environment or other animals or personnel during hospitalization.
  • Veterinary personnel are considered the most common mode of transport for hospital-associated infections.
  • Infections are considered as hospital-associated if they first appear 48 hours or more after hospital admission or within 30 days after discharge. This cutoff is somewhat subjective, but it is widely used in human and veterinary medicine to determine the source of infections once hospitalized.
  • Not all infections that develop during hospitalization are hospital-associated. Some cats maybe incubating community-associated infections, which are expressed after admission.
  • Generally, infections that occur within 48 h of admission to a hospital are considered community-associated, however it is possible that some hospital-associated infections could develop within this timeframe and that some community-associated infections could take longer to develop.
  • Similarly, not all hospital-associated infections are noticed during hospitalization. Cats can be infected while in hospital but not develop clinical signs of infection until after discharge. Typically, infections that occur within a certain period of time (~30days) of discharge from hospital are considered hospital-associated/community-onset infections. 
  • Hospital associated infections are of particular concern because the patients immunity may be compromised by underlying disease, drugs, surgery, invasive supportive care, malnutrition or stress.
  • Cats can be exposed to a variety of infectious agents in veterinary hospitals including those from contaminated environments, veterinary personnel or other infected animals.
  • Hospital-associated infections are an inherent risk of hospitalization. Development of a hospital-associated infection does not necessarily indicate a poor quality veterinary clinic. A certain percentage of hospital-associated infections are considered non-preventable and would occur despite the best infection control program. Infection control programs are designed to reduce the preventable fraction of hospital-associated infections. 
  • Organisms endemic to the hospital environment often show multiple drug resistances Resistant bacterial infections and may lead to outbreaks of infection. Examples include multi drug resistant E.coli  Escherichia coli, methicillin-resistant Staphylococcus aureus (MRSA) Methicillin-resistant Staphylococcus aureus.
  • Hospitals for all species contain individuals of varying levels of susceptibility and animals are often crowded together in a situation in which they are likely to encounter agents of infectious disease.
  • For details of biosecurity and infection control procedures used in small animal hospitals, see Biosecurity and Infection control Biosecurity and infection control.
  • Hospital-based human epidemics of staphylococcal infections, including multi-resistant strains, have been reported since the 1950s and encouraged the development of hospital infection control policies.
  • Hospital-associated infections are an important cause of morbidity and mortality in humans. As medical advances in human medicine lead to increased survival from serious diseases, there still remains those that are immunocompromised and with increasing numbers of hospital visits, hospital-associated infections become a greater risk.
  • Similarly, advances in small animal medicine have resulted in more invasive procedures, such as intravenous and urinary catheters, advanced surgical procedures, an increase in duration of hospitalization, an increase in intensive care practices, and the increased use of antimicrobial drugs Therapeutics: antimicrobial drug, all of which inherently increase the risk of hospital-associated infection. 
  • Many different organisms have been implicated in hospital associated infections of cats. Some are thought to be intrinsically pathogenic, such that a certain number of animals exposed to the pathogen will develop clinical signs. Eg feline herpesvirus Feline herpesvirus disease or feline calicivirus Feline calicivirus disease, which can exist in a small number of carrier animals but can cause clinical illness in a proportion of the population, particularly in stressed animals.
  • Other organisms that might be considered normal resident flora on the skin, in the upper respiratory tract, or in the gastrointestinal tract can become pathogens that is if they gain access to normally sterile parts of the body, if they become a dominant organism (as in bacterial overgrowth), or if they are resistant to antimicrobial drugs Feline herpesvirus disease.
  • Common nosocomial infections in cats in the veterinary hospital include surgical wound infections, infectious upper respiratory tract disease (URTD), and urinary tract infections
  • Although the control of infectious diseases in small animal hospitals focusses on contagious infectious diseases, such as URTD Viral-induced upper respiratory tract disease, more recently the control of zoonotic infectious diseases such as MRSA have taken precedent.
  • Some hospital-associated infections are highly contagious, often brought in by infected cats, and appear as epidemics, for example URTD, caused by feline herpesvirus (FHV) and/or feline calicivirus (FCV) or virulent systemic disease caused by FCV (FCV-VSD) Feline calicivirus (new strains).
  • Others are caused by agents already present in cats and veterinary personnel and which can contaminate the hospital environment, eg MRSA.
  • Many of the problems found in small animal hospitals are similar to, and have similar risk factors to those widely reported in human hospitals, such as hospital-associated infections involving MRSA.

Surveillance and monitoring of hospital-associated infections

  • Surveillance is defined as "the ongoing, systematic collection, analysis, and interpretation of health data essential to the planning, implementation, and evaluation of public health practice, closely integrated with the timely dissemination of these data to those who need to know".
  • Annual comparisons of the incidence of hospital-associated infections is a useful monitor of infectious diseases, however changing patterns of diseases can make it difficult to correlate disease rates with infection control program quality. It is important to establish a baseline level of infection against which trends can be identified and changes in the profile of nosocomial infectious organisms detected.
  • The objectives of a surveillance program for hospital-associated infections are: 
    • To evaluate the effectiveness of infection control and biosecurity measures.
    • To assess compliance with infection control measures.
    • To provide a basis for modifications to the infection control program.
    • To assess the cost-effectiveness of the infection control program and encourage optimal allocation of resources.
  • Components of a surveillance program for nosocomial pathogens include:
    • A risk-based assessment of the priorities for surveillance (see Risk assessment in Biosecurity Biosecurity and infection control).
    • Estimating the incidence rate of hospital-associated infection or diseases.
    • Estimating the prevalence of shedding of pathogens.
    • Evaluation of prevalence and relevance of environmental contamination.
    • Establishment of thresholds or critical limits that, when exceeded, trigger further action.
    • Formal or informal audit of procedures to ensure compliance.
    • Feedback of the results of surveillance to hospital personnel.
    • Regular review and modification of procedures.
  • Surveillance may be active (samples are collected specifically for the purposes of surveillance) or passive (using samples submitted for diagnostic testing).
  • Syndromic surveillance uses clinical diagnosis, ie cough/fever/diarrhea, to indicate probable cases.
  • Surveillance may be continuous or periodic.
  • Targeted surveillance focuses on the patients and procedures associated with the greatest risk of infection or carriage of particular infectious agents and can reduce the cost of a surveillance program.
  • Surveillance programs in human hospitals typically use highly standardized case definitions for each hospital associated pathogen.
  • Surveillance of the hospital environment for bacterial organisms is often used as the basis to assess the effectiveness of general isolation, hygiene, and cleansing and disinfection procedures, eg surveillance of MRSA in hospital environments has been carried out. 
  • Molecular typing methods, such as genetic sequence typing, pulsed-field gel electrophoresis (PFGE) or multilocus sequence typing (MLST), may be used in outbreak investigations to study the epidemiology and relatedness of the organisms isolated and to clarify transmission pathways. Any of these typing methods must be analysed concurrently with epidemiological data for proper interpretation of results. 
  • Clients should be informed of the surveillance program, and their consent obtained for collection of samples if necessary.
  • The incidence and overall impact of hospital-associated infections in veterinary hospitals is not very well known, however, the factors contributing to the increase in nosocomial infections in human hospitals are becoming more common in veterinary medicine.
  • Whilst outbreaks, especially of MRSA, receive significant attention, most hospital-associated infections are probably sporadic infections, such as URTD in cats that receive much less attention. 

Hospital-associated infections in small animal practice

  • In small animal veterinary practices/hospitals the most common type of hospital associated infections appears to be post-operative/surgical wound infections.
  • Other hospital associated infections include urinary tract infections (UTI) following repeated catheterization, blood stream infections, and respiratory disease.
  • There is limited data on hospital associated infections in cats compared to that of dogs.
  • Since many of these infections are associated with multi-drug resistance, it is important to ascertain the circumstances by which they arose, including assessment of surgical/invasive procedures as well as area of the practice/hospital in which the affected animals are hospitalized.

Hospital-associated post-operative wound infections

  • Post-operative wound infections are a major contributing factor to increased morbidity and prolonged hospitalization, added expense and surgical failures.
  • The seriousness of a post-operative infection is generally related to infection location, and such infections can be associated with significant morbidity and mortality.
  • Infection occurs more commonly in emergency than elective procedures and in orthopedic surgery or when foreign material is present in the wound.
  • Most wound infections become established at the time of surgery, or within a couple of hours of contamination, but bacterial contamination does not have to lead to the establishment of infection.
  • Wound infections are the most common type of hospital-associated infection reported in small animals.
  • The development of post-operative infection depends on:
    • The patients immune system and other defences, including both the innate (nonspecific) and the adaptive (specific) systems.
    • The environment of the wound and surgical preparation.
    • The use of antimicrobials. 
    •  The surgical procedures performed, especially those of prolonged duration, and surgical technique.
    • Environmental contamination/fomite spread of the organism.
  • Agents causing post-operative wound infections are usually commensals of the skin, gastrointestinal tract or mucous membranes of the patient, or from the environment, personnel or equipment in the surgery.
  • The major infectious agents involved in hospital-associated post-operative wound infections in feline patients are:
  • The duration of antimicrobial therapy after surgery is controversial, but may be a factor encouraging the development of antimicrobial resistance in such organisms as staphylococci. Often, continuation of antimicrobials after surgery is unnecessary.
  •  Staphylococcus pseudointermedius, a commensal of the skin, nasal cavity and intestinal tract of up to 50% of healthy dogs (found in a lesser extent in cats), is also responsible for causing skin and soft tissue infections.
  • MRSP, a form of S. pseudointermedius, is highly resistant to beta-lactam antibiotics, and appears to be increasing in prevalence, particularly in canine infections.
  • Although MRSP colonization is uncommon in healthy dogs and cats, routine use of good hygiene and biosecurity should be implemented to prevent spread within the hospital environment.

Hospital-acquired urinary tract infections

  • Hospital-associated UTIs can originate from an animals gut flora via perineal or periurethral contamination, from animals co-hospitalized, from veterinary personnel or from the hospital environment.
  • One of the most important risk factors for the development of UTIs in the placement of urinary catheters.
  • Catheter-associated bacteriuria has been well documented in both dogs and cats.
  •  E. Coli is the most frequent pathogen associated with UTIs.
  • Many of the E.coli isolated from hospital-associated UTIs are associated with multi-drug resistance
  •  E.coliproducing extended spectrum beta-lactamases (ESBLs) are predominantly found in UTIs and can be passed into the environment from humans.
  • Most ESBL producing organisms are multi drug resistant Resistant bacterial infections.
  •  E.coli carrying an ESBL were first detected in livestock in the UK in calves with diarrhea in 2004.
  • Risk factors for development of multi-drug resistant E.coli include the length of hospitalization, ie the longer the stay in hospital (particularly in ICU) the more at risk the patient would be for developing a multi-drug resistant E.coli infection.
  • It is suggested that hospitalization should be as short as possible to limit/prevent the development of antimicrobial resistance among E.coli
  • Other pathogens associated with UTIs include KlebsiellaStaphylococci spp, Streptococcus spp  Streptococcus sppProteus mirabilis Proteus spp, and Pseudomonas Pseudomonas spp.

Hospital associated blood-stream infections

  • Pathogens can enter the bloodstream as a severe complication of infections, during surgery or as a result of invasive therapies (such as catheterization).
  • In extreme cases the immune response to the bacteria can cause sepsis and septic shock Shock: septic.
  • The main pathogens associated with hospital-associated blood-stream infection include E.coli, and MRSA.

Other significant hospital associated pathogens

  • One of the main hospital associated infections in cats is outbreaks of respiratory disease.
  • Respiratory pathogens (many of these organisms can also be spread by fomites):
    • Feline herpesvirus (FHV) Feline herpes virus: feline rhinotracheitis virus.
    • Feline calicivirus (FCV) Feline calicivirus.
    • Both of these pathogens can be excreted into the hospital environment by asymptomatic carriers, and can result in outbreaks of disease.
    • Feline herpesvirus carriers will shed virus in response to stress.
    • Of particular significance are hospital-associated outbreaks of virulent systemic FCV (FCV-VSD) that have been associated with high levels of mortality and morbidity.
    • Clinical signs associated with FCV-VSD infection include depression, fever, anorexia, edema of the face and limbs, cutaneous ulceration, jaundice, oral ulceration and URTD.
    • Vaccination against FCV does not protect against infection or the development of clinical disease.
    • Hospital-associated outbreaks of FCV-VSD have been reported in North America, Europe and the UK. This paper describes the first outbreak identified in France. The severity of FCV-VSD is likely to lead to hospitalization and its highly contagious nature accounts for rapid spread of the virus within and outside the hospital through people carrying the virus.
  • Enteric pathogens:
    •  Clostridium difficile Clostridium difficile:
      •  C. Difficileis a gram positive environmental organism that has been associated with a number of hospital-associated infections in dogs, however, there is limited data to assess its relevance in feline hospital-associated infections.
      •  Salmonella Salmonella spp:
        • Hospital-associated outbreaks of feline salmonellosis ( Salmonella typhimurium) have been reported. In most cases the outbreaks have been associated with both human and animal infection within veterinary clinics or animal shelters.

Zoonotic diseases

  • Exposure to zoonotic agents is common in veterinary practice.
  • Many organisms that are associated with hospital infections are zoonotic, ie transmissible from animals to humans and vice versa.
  • Many zoonoses, require direct contact for transmission, whereas others, can be transmitted indirectly by contact with contaminated fomites or the environment.
  • Veterinarians have a responsibility to protect other personnel and clients from exposure to zoonotic pathogens.
  • Particular care should be exercised when veterinary personnel or animal owners are immunocompromised.
  • MRSA is an important zoonotic hospital-associated pathogen and can be transmitted in both directions between humans and other species. 
  •  Clostridium difficile is an anaerobe Anaerobic bacterial infections: overview that causes diarrhea in many species. Zoonotic transmission may be possible, particularly to personnel who are immunosuppressed or receiving antimicrobial therapy. Periodic cleansing of the hospital environment with a 5% solution of bleach should reduce contamination with this agent, however it is unclear whether this will have any impact on the potential for transmission.
  • Other diseases, such as ringworm Dermatophytosis have been associated with zoonotic transmission to humans from cats.
  • Links should be established with the appropriate public health authorities if hospital-based zoonotic infections are encountered. It must be noted that healthcare personnel are often not trained to recognize the clinical signs of zoonoses.
  • Veterinary personnel should ensure that their physician knows that they work in the veterinary field.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Gibson J S, Cobbold R N, Trott D J (2010) Characterization of multidrug-resistant Escherichia coli isolated from extraintestinal clinical infections in animals. J Med Microbiol 59 (Pt 5), 592-598 PubMed.
  • Weese J S, Finley R, Reid-Smith R R et al (2010) Evaluation of Clostridium difficile in dogs and the household environment. Epidemiol Infect 138 (8), 1100-4 PubMed.
  • Gow A G, Gow D J, Hall E J et al (2009) Prevalence of potentially pathogenic enteric organisms in clinically healthy kittens in the UK. J Feline Med Surg 11 (8), 655-662 PubMed.
  • Philbey A W, Brown F M, Mather H A et al (2009) Salmonellosis in cats in the United Kingdom: 1955 to 2007. Vet Rec 164 (4), 120-122 PubMed.
  • Reynolds B S, Poulet H, Pingret J L et al (2009) A nosocomial outbreak of feline calicivirus associated virulent systemic disease in France. J Feline Med Surg 11 (8), 633-644 PubMed.
  • Benedict K M, Morley P S, Van Metre D C (2008) Characteristics of biosecurity and infection control programs at veterinary teaching hospitals. JAVMA 233 (5), 767-773 PubMed.
  • Clooten J, Kruth S, Arroyo L et al (2008) Prevalence and risk factors for Clostridium difficile colonization in dogs and cats hospitalized in an intensive care unit. Vet Microbiol 129 (1-2), 209-214 PubMed.
  • McLean C L, Ness M G (2008) Meticillin-resistant Staphylococcus aureus in a veterinary orthopaedic referral hospital: staff nasal colonisation and incidence of clinical cases. J Small Anim Pract 49 (4), 170-177 PubMed.
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