Ongoing: Single point-in-time retrospective surveillance is useful but provides limited clinically relevant information for long-term use. What has happened in the past does not continue in the future, and current knowledge is usually more important than knowledge of prior events.

Systematic: Data that are not collected in a systematic manner may be subject to bias, which limits the usefulness of the data and can potentially lead to inappropriate conclusions or ineffective interventions.

Analysis: Data are useful only if analyzed. Some surveillance programs fail because no one looks at the collected data. It makes no sense to collect data that are not going to be analyzed.

Interpretation: Determination of the clinical relevance of analyzed data is critical. Calculation of rates and associations is important but must be considered in a clinical context for appropriate responses to be undertaken. Infection control surveillance has to be more than academic epidemiologic analysis; it needs to be clinically useful.

Dissemination: The best infection control program will fail if information is not properly communicated. Data collection, analysis, and interpretation can identify important issues, but without a plan to effectively communicate this to relevant individuals or groups, efforts spent designing, implementing, and analyzing data will be less effective than they could otherwise be.

Purpose of Surveillance

The first step that should be taken when surveillance activities are considered or assessed is to clearly define the objectives of the surveillance program. In the broadest terms, surveillance programs are designed “to reduce morbidity and mortality and to improve health.”¹⁷ In a veterinary hospital, this includes both hospital-associated (nosocomial) infections in patients and zoonotic infections in staff and pet owners. Determination of endemic (Table 15-1) disease rates is a key component of surveillance, as it allows for objective assessment of current practices, raises awareness, identifies areas for potential improvement, and facilitates identification of outbreaks. Data regarding endemic rates are also needed for assessment of the impact of newly implemented infection control measures. An understanding of endemic disease rates is required for prompt identification of disease occurrence in excess of the endemic disease rate (i.e., an outbreak) because a “higher-than-normal” rate is difficult to identify when the “normal” rate is not known, and therefore may not be identified until it is quite advanced and more difficult to control. Surveillance can also be useful for education and compliance purposes. Because infection control practices are often inherently cumbersome and inconvenient, poor compliance is often a problem and is often the most important weakness of any infection control program. Objective data provided through surveillance along with regular feedback can be used to help persuade hospital personnel to adopt and maintain recommended practices.⁶ A potentially overlooked benefit of surveillance is satisfying regulators and proving “due diligence.”⁶ Hospital-associated and zoonotic infections are an inherent risk in veterinary hospitals, but hospitals have a responsibility to take reasonable precautions to reduce the risk of these events. As more information becomes available about hospital-associated infections, zoonotic infections, and infection control, the expected standard of care is increasing. Although an infection that develops in a veterinary hospital does not necessarily indicate malpractice or any form of liability (because a significant percentage of infections are not preventable by using best practices), failure to take reasonable measures to reduce the risk of infection could be construed as such. Therefore, implementation and documentation of a reasonable infection control program, including basic aspects of surveillance, are important in demonstrating that the expected degree of diligence and care has been taken.

Surveillance in Human Medicine

The landmark Study of the Efficacy of Nosocomial Infection Control project (SENIC)⁸was the first broad, coordinated assessment of infection control practices in human hospitals and is still a key determinant of infection control practices. This study evaluated aspects of infection control with respect to their impact on infectious disease rates. Three main components of infection control were described: ongoing surveillance of infections, active control efforts, and qualified staff members. A key finding was that infection rates in hospitals without an effective infection control program increased by 18% over 5 years, while rates decreased by 7% to 48% in hospitals with a very effective program. When one considers the number of hospital-associated infections that occur each year (estimated 1.7 million infections and 99,000 associated deaths in the United States each year)³ and the associated costs (in excess of a billion dollars per year), it is clear that infection control is a critical factor for delivery of optimal, or even adequate, patient care.

Surveillance is now a key and sometimes mandated infection control activity in human hospitals. Surveillance efforts vary between hospitals and between regions as a result of many factors such as endemic disease rates, hospital facilities, public and regulatory pressure, finances, and the presence or absence of key individuals driving development of surveillance programs. Common surveillance practices include routine review of culture reports and investigation of specific infections, routine review of charts of hospitalized patients by infection control personnel, evaluation of new reports of fever or other syndromes, collection of data from specific infection control forms completed by ward personnel, and review of charts of discharged patients.⁶ Active surveillance is becoming more common for high-risk and high-profile pathogens such as MRSA, vancomycin-resistant enterococci (VRE), and Clostridium difficile, whereby selected patient populations are automatically screened for colonization at the time of hospital admission.^2,15,18,26 Active screening for MRSA has been an effective part of MRSA control in many hospitals by allowing for prompt identification and isolation of carriers, and reducing exposure to staff and other patients.²⁶ On-demand screening for pathogens is also used as a common outbreak control measure, whereby samples are collected from all, or just potentially exposed, patients in the midst of an outbreak or potential outbreak. Surveillance is also an important component of surgical site infection control. Establishment of a strong infection surveillance and control program has been demonstrated to be an effective surgical site infection control measure⁸ and is one that should be in place in all facilities.

Surveillance in Veterinary Medicine

The field of hospital infection control is very much in its infancy in veterinary medicine, and correspondingly little objective information is available regarding veterinary hospital surveillance. Most formal surveillance activities in veterinary hospitals have involved horses, and information regarding small-animal hospitals is profoundly lacking. Accordingly, surveillance decisions for small-animal practices are based primarily on extrapolation from human medicine and horses, in combination with knowledge of small-animal infectious diseases and general principles of infection control. Although many of the practices and challenges in small-animal veterinary hospitals are certainly different from those in human hospitals, many basic infection control concepts are equally applicable. Although it is hoped that objective, small animal–specific information will become available, currently available information from other areas allows for development of logical, if unproven, surveillance efforts. However, for veterinary infection control to advance, specific efforts are required. Early infection control and surveillance priorities in human medicine included development of standard definitions for hospital-associated and community-associated infections, preparation of recommendations for hospital-wide infection surveillance, establishment of standardized training programs for infection control personnel, and determination of hospital-associated infectious disease rates.¹⁹ All these activities are required for small-animal veterinary medicine.

Passive Surveillance

Passive surveillance is a practical, efficient, and cost-effective tool that can, and should, be implemented in every veterinary clinic. This form of surveillance involves the use of data that are already available, such as medical record data, admission data, bacterial culture and susceptibility testing results, and other types of diagnostic testing data. This is termed “passive” surveillance because these data are already available from the clinical management of cases, as opposed to “active” surveillance, which involves collection of data specifically for infection control purposes. Beyond simply having these data somewhere in a medical record system, passive surveillance involves the organized collection and analysis of predetermined aspects of available data to determine elements such as endemic disease rates, antimicrobial susceptibility patterns and trends, and changes in disease patterns. Passive surveillance can also be used to ensure that unusual or particularly difficult diagnoses from a nosocomial or zoonotic standpoint (e.g., MRSA, canine parvovirus) are rapidly identified and conveyed to relevant individuals, so that appropriate measures can be taken.

As with any aspect of surveillance, simply collecting data is of no use if no one analyzes it, or if no plan is devised for using the results. Therefore, passive surveillance must be an organized, structured activity with clear objectives and methods.

In the absence of an ongoing infectious disease outbreak, passive surveillance is likely adequate for most clinics. An example of passive surveillance would be monitoring surgical site infection rates (see Chapter 10 for definition of surgical site infection) involving overall procedures or, ideally, overall rates plus specific rates for common or high-risk procedures (e.g., tibial plateau leveling osteotomy, intestinal resection and anastomosis). Critical limits for specific hazards can be established, with a predetermined plan of action should limits be exceeded.¹⁹ For example, a surgical site infection rate in excess of a predetermined number could automatically trigger an investigation to determine whether an outbreak is under way and/or if specific measures need to be undertaken.

Another passive surveillance activity that can be useful involves collection and analysis of routine culture and susceptibility testing results. Having data about bacterial species isolated from various sites and their susceptibility patterns can be useful in selection of empiric therapy when culture is not possible, or while culture results are pending. With this type of surveillance, a clinician treating a dog with a postoperative wound infection could use those data as part of the decision-making process when choosing initial antimicrobial therapy. The more detailed characterization of surveillance, the better, as this allows for more specific and appropriate application of data. For example, pathogen and resistance patterns may be different in surgical site infections originating in hospital versus the community, and knowing culture result patterns from both origins would facilitate a more direct empiric approach.

Although passive surveillance can be relatively easy and cost-effective, people using the data must understand any limitations. Culture and susceptibility data can provide useful information, but potential biases may be seen in such datasets. If cultures are usually submitted only for recurrent infections or those that have failed initial therapy, a bias toward more resistant pathogens will probably be evident. This does not negate the value of the data; it just means that potential limitations must be considered. To do so, people using the information must understand where the data came from and what limitations may be present.

Monitoring surgical site infection rates must be accompanied by an understanding of the practice and the likelihood that all or most infections will be reported. Most veterinary patients have relatively short hospital stays, often being discharged before the highest risk period for identification of surgical site infection. In human medicine, 20% to 60% of surgical site infections become evident only after discharge.¹¹ Similar data are not available for veterinary medicine, but it is reasonable to assume that a similar, if not greater, fraction of surgical site infections occur after discharge. Therefore, identification of surgical site infections (or other hospital-associated infections) that develop after discharge is very important if meaningful rates are to be calculated. Postdischarge surveillance can be problematic, depending on the practice type. In typical primary care small-animal clinics, most patients likely return for suture removal and rechecks, and identifying postdischarge complications should be relatively easy. This may be more problematic in referral hospitals, where rechecks are sometimes performed by the referring clinic. If the referral hospital is not notified about complications that are identified by the referring veterinarian, which could be particularly common with mild complications, surgical site infection rates would be underestimated. Therefore, effective communication between referral and referring hospitals is critical. Similarly, clusters or outbreaks of surgical site infections can develop in emergency clinics without notice because the infected animals would be returned to various primary care practices, and communication between these practices and emergency clinics is often limited. Emergency clinics are also perhaps less likely to have a formal infection control program, further complicating the problem and potentially increasing the risk that outbreaks may go unnoticed until they are very large.

Monitoring antimicrobial use practices through review of prescription data or individual medical records can provide information about prudent and effective use (drugs, dosing, duration). This is unlikely to be practical or effective as a routine surveillance tool and is, at best, reserved for periodic use to evaluate current practices or in response to specific concerns about antimicrobial use.

Active Surveillance

Active surveillance involves gathering data specifically for infection control purposes. Therefore, it is usually more expensive and time-consuming but, if properly done, can provide the highest quality data. Active surveillance can involve patients, medical equipment, or the environment. Environment and equipment surveillance are described in greater detail later.

Active surveillance of patients usually involves screening of patients for infection or colonization with specific pathogens. As with other aspects of surveillance, active surveillance must be performed using an organized, predetermined program designed to fulfill specific objectives, with associated plans for analysis of data and use of results. Broad, routine active surveillance is rarely indicated in veterinary hospitals and typically is reserved for large facilities with increased infection control threats and personnel available to direct such testing, or during a specific outbreak investigation. Even then, it is of limited routine use. An example of active surveillance is collection of nasal and rectal swabs from all animals being admitted to a hospital, whether or not they have signs of infection, to screen for methicillin-resistant Staphylococcus aureus, as is commonplace in human medicine,2,15,20 and as has been described for equine patients.²⁴ This typically involves screening of patients (all patients or selected high-risk groups) at the time of hospital admission to identify carriers. Screening allows for isolation of carriers and decreases risk of transmission to other patients or health care personnel. It also may indicate patients at increased risk for developing clinical MRSA infection, and in humans it is used in some areas to identify people for decolonization therapy.⁹ Therefore, this type of surveillance clearly has specific objectives, a defined plan, and a predetermined response to the results. Admission screening has been a key component of MRSA control in many countries, and much time, effort, and money are expended because of the overall medical and economic benefits that come with reduced infection rates. MRSA is an emerging problem in veterinary medicine, and increasing community-associated MRSA colonization in pets may lead to a need for active surveillance in some regions. The author is unaware of any institutions that perform ongoing surveillance in small animals for infection control (not research) purposes; no evidence indicates that routine active surveillance is currently indicated. No standard guidelines indicate when active surveillance should be implemented, and factors such as infection pressure (prevalence of MRSA in the patient population), patient risk (type of caseload), infection rates (whether MRSA infections are a problem), and occupational health concerns must be considered.

Because of the cost and time required for active surveillance, a targeted approach can be considered, whereby surveillance efforts are directed against certain populations rather than the entire hospital population. The effectiveness of targeted versus complete active surveillance is unclear and is a controversial area in human medicine. Targeted approaches are easier and less expensive but are dependent on a clear understanding of relative risks between different groups, the ability to clearly define groups and identify those at higher risk, and whether diseases will behave as expected, all of which can be problematic at times. Therefore, targeted surveillance offers many of the benefits of active surveillance with lower costs, but it has the potential to overlook or underestimate problems if the targeted population is suboptimal, or if the disease does not follow expected patterns.

Personnel observation is a form of active surveillance, but it is best used as a research tool rather than as a routine infection control measure. Standardized monitoring of activities such as hand hygiene compliance, surgical scrub technique, and general clinical practices can provide interesting information, but given factors such as difficulties with objective and standardized collection of data and ethical issues involving observation of compliance, such measures are not recommended.

Because of the cost and time required for active surveillance, need must be clearly indicated, and meaningful data must be available for collection and analysis. Rarely will active surveillance be required in primary care veterinary hospitals. Consultation with specialists in infectious disease, infection control, and/or microbiology is strongly recommended before any active surveillance program is instituted.