_______________________________________________________________ Healthcare-Associated Infections
Case Example The following case outlines an investigative process and illus- trates that the source of an outbreak may be unusual [341]. A cardiac surgeon noticed a cluster of cases of sternal wound dehiscence among his patients who had had surgery. Specimens from the wounds were obtained for culture. Microbiologic evaluation indicated that the infections were predominantly caused by Enterobacter cloacae, and molecular typing and serotyping demonstrated that the isolates were similar. No infections had developed after operations the surgeon had performed at other hospitals. No breach in aseptic technique was identified. All of the infected patients had been operated on in the same operating room, and the environment was screened. No source was found. Further questioning of the surgeon’s operative practice revealed one difference from other cardiac surgeons: he used semi-frozen sodium lactate solution to achieve cardioplegia. Swabbing of the freezer used for the solution identified E. cloacae of the same typing as that found in the wound infections. The hypothesis was that contamina- tion of the freezer led to contamination of the ice/slush solution, and the micro-organism was transmitted to the patients. The freezer was replaced, a rigorous cleaning schedule was instituted, and no further cases have occurred. Potential Outbreaks The following are overviews of selected potential outbreaks. Identification and early action in the case of any of these outbreaks will limit the adverse effects. Group A Streptococci Most outbreaks of group A streptococci involve surgical wounds, and the source can usually be traced to an asymptom- atic carrier in the operating room or on the wound care team [89; 342]. Standard Precautions are sufficient if the wound is minor; if it is major, Contact Precautions should be instituted and followed for 24 hours after initiation of effective therapy [25]. The healthcare worker should receive antimicrobial therapy as appropriate and leave the setting until completion of therapy. Pulmonary Tuberculosis Dealing with pulmonary tuberculosis involves prompt iden- tification of the disease and determining the susceptible individuals who were exposed to the patient before isolation [89]. Airborne Precautions should be instituted and remain in place until the patient is receiving effective therapy, is improv- ing clinically, and the culture results for three consecutive sputum specimens, collected on different days, are negative. Comprehensive information is available in the CDC guidelines for preventing the transmission of tuberculosis in healthcare facilities [343].
An outbreak should be identified and investigated as early as possible to prevent morbidity and mortality. Any healthcare professional who suspects an outbreak should notify infection control staff, and an outbreak team should be established. Investigating an outbreak involves [18; 338]: • Establishing the existence of an outbreak • Verifying the diagnosis • Defining and identifying cases • Describing and orienting the data in terms of time, place, and person • Developing and evaluating hypotheses • Refining hypotheses and carrying out additional studies • Implementing control and prevention measures • Communicating findings The outbreak team should collaborate with all appropriate healthcare workers to identify either the carriers or the com- mon sources of the infection and to review aseptic practices and disinfectant use for a breach in compliance. Data on potential cases should be reviewed and a case definition should be developed. The case definition should include [18; 338]: • Unit of time and place • Specific biologic and/or clinical criteria • Inclusion/exclusion criteria • Gradient of definition (definite, probable, or possible) • Differentiation between colonization and infection • Specific criteria to identify the index case, if relevant information is available Data should be collected from all available sources, such as patient charts, microbiology reports, pharmacy reports, and log books from patient units. Describing the outbreak in terms of individuals, place, and time helps to create an epidemic curve, which shows the distribution of cases by time of onset [18]. An attack rate can then be defined as the number of people at risk who are infected compared with the total number of people at risk. Developing and evaluating hypotheses will yield the source of the outbreak and/or the index case. The data should be reviewed carefully to evaluate the characteristics and similari- ties among affected individuals. The team must then determine the extent of the outbreak. Cohort isolation is implemented as needed ( Table 21 ) [25; 339]. Throughout the investiga- tion, the team should communicate routinely with hospital administration. At completion, data on the outbreak should be documented and published, as the information can provide valuable education to the healthcare community at large and can help staff prepare for future outbreak investigations [340].
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