Audrey Ruple, Nathan M. Slovis and Barbara Jones
"First do no harm." This edict reminds all veterinarians that they must consider the possible harm that might be caused by any intervention. Since as early as 1860, this phrase among veterinarians has been an expression of hope, intention, humility, and recognition that acts with good intentions may have unwanted consequences. The vast majority of patients who have access to medical services today are healed. There are some, however, who suffer unintended consequences of care, such as health care–associated infections (HAI). To ensure that such life threatening–life saving care does not result in HAI, modern health care has developed an extensive system for infection prevention. Regardless of the approaches taken, health care facilities must strive for 100% adherence to the institutions' infection control strategies. To achieve this caliber of adherence, proper education of the staff will be necessary.
The focus of this chapter is to educate readers to be proactive when it comes to biosecurity attentiveness to safeguard patients, clients, students, co-workers, animal companions, and the community from potential infectious agent(s). Recognizing the need to establish objectives, expectations, and goals for a successful biosecurity program will in turn lead to quality standards of care delivered by a dedicated and educated team.
DEFINITIONS OF DISEASE CONTROL TERMINOLOGY
It is important to establish a common vocabulary as many of these words have other meanings or uses in veterinary practice. The way these words and phrases are defined here is specifically in the context of how they relate to infection control. The definitions are compiled from those by the Centers for Disease Control (CDC), World Health Organization, Food and Agriculture Organization of the United Nations, and the Occupational Health and Safety Administration. Table 1.1 provides the definitions of disease control terminology used in this book.
EPIDEMIOLOGIC LEVELS OF DISEASE CONTROL ACTIVITIES
Disease control activities against infectious agents occur at four levels: individual, institutional, community, and global.
The first level, the individual, is predominantly the domain of the primary provider. A variety of prevention strategies can be targeted to individuals through their primary provider, normally a veterinarian providing wellness and general health services. One example is the use of chemoprophylaxis (antibiotics) to help prevent surgery-site infections.
The second level is that of the institution, which is the domain of the infection-control practitioner or the organization health official. This level would include veterinary hospitals, pet boarding facilities, human health care facilities, nursing homes, other human residential facilities, and schools. Programs to prevent the spread of fecal, respiratory, and blood-borne pathogens to health care workers or patients are examples of control strategies targeted at the institutional level.
The third level is targeted to the community (in general) and is predominately the domain of public health agencies (local, state, and national levels). The removal of dead animal carcasses after a hurricane is an example of a control measure targeted for the community.
The fourth level is related to global strategies. For a number of important pathogens, it has become evident that global control strategies are critical to disease occurrence within the United States. Examples of this are the global strategies for bovine spongiform encephalopathy and avian influenza.
Although some control measures are specific for each one of these levels, substantial overlap can occur. For instance, immunization programs operate at all four levels (Osterholm et al., 2000).
TARGETED ELEMENTS FOR DISEASE PREVENTION
The transmission of infectious agents requires three elements: a source (or reservoir) of the infectious agent, a susceptible host with a portal of entry receptive to the agent, and a mode of transmission for the agent. Identification of areas or processes in which transmission of pathogens is likely to occur (control points) and implementation of measures aimed at minimizing the possibility of such transmission, while allowing for reasonable flow and function within the veterinary hospital or animal facility, are important components of biosecurity (Dunowska et al., 2007; Lappin, 2003; Morley, 2002). During the assessment and development of the prevention and control activities targeted to infectious diseases, the weakest link in the chain of infection (agent, transmission, host) needs to be considered for each specific pathogen. In some situations, control of the agent in a specific reservoir may be the best way to reduce disease occurrence. Chlorination of water is an example of destroying an agent in its reservoir or eliminating a possible mode of transmission.
Strategies aimed at the level of transmission need to be tailored to the type of transmission involved. An example of a control activity targeted to airborne transmission is the isolation of the infected animal to a facility where there is no shared airspace or where no other animals are currently housed on the premises. The control of vector-borne transmission can be targeted toward destroying the vector and toward the use of repellents, such as in the case of vesicular stomatitis or West Nile virus outbreaks.
In many instances, the best way to prevent disease occurrence is through modification of the host, such as developing or boosting immunity through active or passive immunization. Other control activities targeted to the host may include improving the nutritional status of a neglected animal or providing chemoprophylaxis (antibiotics) against a variety of agents. Even simple bathing and grooming of animals can help with identification of external parasites and skin conditions. Every effort should be made to minimize the contact between animals with a history or clinical signs suggestive of infectious contagious disease, or those with confirmed contagious disease, and the remainder of the patients or animals at a boarding facility (Traub-Dargatz et al., 2009). Chapter 5 describes strategies for disease prevention in animal facilities.
EVALUATION OF RISK, FEASIBILITY, COST, AND EFFECTIVENESS
Before implementing disease prevention and control strategies, several issues need to be considered, including risk, feasibility, cost, and effectiveness.
Risk Assessment
Risk assessment deals with the probability for potential disease exposure. Epidemiologic studies or analysis of surveillance data can serve to define animals at risk and can also quantify risk within different populations. Information that is needed for making the optimal decisions regarding the risk posed would include history of the arriving animal, history regarding contact of the arriving animal with other animals having contagious disease, pertinent laboratory testing performed prior to arrival, physical findings on initial examination of the new arrival, and pertinent laboratory tests results if available at arrival or soon thereafter (Traub-Dargatz et al., 2009). To help better understand the risks of the animal to disseminate a disease, there is a need for knowledge of the past disease status and exposure status in order to best implement targeted control measures for contagious disease. One method to accomplish this is by the having the owner/authorized caretaker/transporter sign a form and state the past history of the animal in relation to exposure to a specific disorder. The reason for such self-certification is to establish risk level. Without this type of information, those receiving the animal would have no mechanism to gather critical information for those animals that have no overt signs of disease at the time of presentation to the facility. The animal could have had exposure to a contagious disease agent that would pose a substantial risk to other animals in the facility if not managed accordingly (Traub-Dargatz et al., 2009).
Another strategy is an admittance-based system. An admittance-based alert system notifies infection control and clinical personnel about re-admitted or transferred patients with a history of infection or colonization. This system allows for review of policies and procedures to be instituted prior to the arrival of the patient with the infectious disease. This provides for routine assessment of education and training among personnel and can improve infection prevention measures at the facility level (Morley, 2002).
Risk adjustments require collection of pertinent information (i.e., Salmonella in hospitalized patients, surgery-site infections, etc.) about the total population being monitored so that objective data can be used to help direct decisions being made regarding risk assessments. These risk adjustments are important because policies and procedures will need to be updated based on these findings.
Feasibility
In developing control programs, the feasibility of a policy also needs to be assessed. Feasibility or practicality of the policy is dependent not only on the sociodemographic factors but also on the operating needs of the facility. For instance, equine facilities that buy and sell horses on a routine basis might accept the risk of contagious disease outbreaks, such as Streptococcus equi, as the norm, instead of isolating newly arrived horses for a period of time required. Animal control shelters face many challenges and risk factors with overcrowding, stress and decreased immune status of animals, and continually changing populations. The risk for infectious disease cannot be totally eliminated, but steps to minimize introduction and spread are addressed regularly (Petersen et al., 2008).
Cost
Cost and availability of resources also need to be considered when developing control strategies. Implementing and maintaining even the most basic biosecurity program requires trained personnel and an adequately staffed facility with appropriate supervision. Outbreak investigations have indicated an association between infections and understaffing; the association was consistently linked with poor adherence to hand hygiene (Harbarth et al., 1999; Fridkin et al., 1996; Vicca, 1999). The understaffing of human nurses facilitates the spread of MRSA in intensive-care settings through relaxed attention to basic control measures (Vicca, 1999).
Effectiveness
Finally, control strategies need to be evaluated for their effectiveness. For example, the effectiveness of the control strategy is a critical issue in evaluating ways to curb salmonellosis in equine care facilities. Cost-effectiveness models are often used in making recommendations for population-based vaccine programs. Challenges to prevention include measurement of outcomes that may be complicated by diagnostic limitations. An example of this is the diagnosing of ventilator associated pneumonia in humans.
PREVENTION INTERVENTIONS
Prevention strategies for infectious diseases can be characterized by using the traditional concepts of primary, secondary, or tertiary prevention. Primary prevention is defined as the prevention of infection by personal and community-wide efforts. Secondary prevention includes measures available to individuals and the population for detection of early infection and effective intervention. Tertiary prevention consists of measures available to reduce or eliminate the long-term impairment and disabilities caused by infectious diseases (Osterholm et al., 2000).
Primary Prevention
An example of primary prevention is immunoprophylaxis, which can be classified as active or passive. Active immunization involves the administration of all or part of the microorganism, live or inactivated (canine distempter vaccine is a modified live virus), or a product of the microorganism (toxoid) to alter the host by stimulating an immune response aimed at protecting against infection. Active administration is also used in postexposure situations, including immunization after exposure (e.g., tetanus). Some vaccines may be given in conjunction with an antitoxin in the postexposure setting. Passive immunization involves the administration of preformed antibodies, often to specific agents, after exposure. The common forms of passive immunization may be hyperimmunized plasma for a foal with failure of passive transfer or botulism hyperimmunized plasma. Human rabies immunoglobulin used for postexposure to a possible rabid animal is another example of passive immunization.
A second type of primary prevention is antimicrobial prophylaxis, often referred to as chemoprophylaxis. Use of effective chemoprophylaxis requires that the infectious agent be susceptible to the antimicrobial used. When used as a primary prevention, the medication may be used before or after exposure in order to prevent infection. Examples of chemoprophylaxis in the postexposure setting include treating with azithromycin for Rhodococcus equi infections or metronidazole for Clostridium perfringens enterocolitis. Prophylaxis against surgical wound infections with broad-spectrum antimicrobials coverage before surgery is an example of chemoprophylaxis in a hospital setting. In many situations, chemoprophylaxis is used because the likelihood of exposure to pathogenic organisms is present, even though proper documentation of exposure is not clear.
Secondary Prevention
Secondary prevention activities entail chemoprophylaxis for active infections and involve the identification of early or asymptomatic infection with subsequent treatment so that infections are eradicated and the sequels are prevented. Although most secondary prevention programs involve intervention at the individual level through the use of chemoprophylaxis, such programs often operate within the context of a population-based or institutional-based screening effort. Most hospital infection control policies include the judicious use of antimicrobials, and many hospitals actually have a committee that establishes policy or outlines issues related to the judicious use of antimicrobials. This may include the exclusion of specified antimicrobials on food animal species, the consideration of reserving certain antibiotics for particular infectious etiologies or presentations, avoidance of use of certain drugs that are considered "big guns" in the human public health realm to avoid the development of antimicrobial resistance in specific populations of bacteria or viruses, and the establishment of minimum therapeutic doses, acceptable routes of administration, or application of minimum inhibitory concentration (MIC) result information from antimicrobial sensitivity testing of culture specimens, when available. An example of secondary prevention would be the use of procaine penicillin or ceftiofur on horses that test positive for Streptococcus equi on a nasopharyngeal screening wash during a farm outbreak of the disease.
Tertiary Prevention
Tertiary prevention efforts involve measures to eliminate long-term impairment and disabilities from existing conditions. Since most infectious diseases are treatable, tertiary prevention activities are less common. This concept is applicable to control some viral infections that are chronic and cannot be eradicated. The use of antimicrobial prophylaxis against possible other opportunistic agents is an example of tertiary prevention activity (Osterholm et al., 2000).
INFECTION CONTROL: STANDARD OPERATING PROCEDURES
Infection control plans, protocols, procedures, and policies are an essential component of disease prevention management (hereafter referred to as plans). These plans must be written, posted, and continually enforced by a designated staff member in order to be effective in preventing infection transmission between patients, between patients and the environment, and between patients and personnel caring for those patients.
There are many considerations to take into account when setting up or modifying an infection control plan, and different areas may need to be emphasized depending on the individual needs of the practice, institution, or animal facility. To be effective, an infection control plan must first identify which infectious agents need to be controlled, which in turn is dependent on the demographics of the patients (small animals vs. dairy), the type of practice or facility (small private practice vs. tertiary referral hospital), location (both geographically and rural vs. urban), public health concerns, and cost of control.
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