Title/Description: Outbreak Investigation Guidelines Department: All Departments. Effective Date: 4/97 REVISED: 1/00, 5/08 I.

Transcription

1 Title/Description: Outbreak Investigation Guidelines Department: All Departments Personnel: All Personnel Effective Date: 4/97 REVISED: 1/00, 5/08 I. PURPOSE At Springhill Medical Center (SMC) an outbreak is considered an increase in occurrences of a complication or disease above the normal limits for this institution. An outbreak may be one episode of a rare occurrence or many episodes of a common occurrence. To control and prevent further disease/infection, an outbreak investigation will be instituted. The goal of an outbreak investigation is to decrease risk of exposure to patients, healthcare workers, visitors and family and to identify factors that contributed to the outbreak. II. POLICY The Infection Prevention and Control Director will determine when a cluster of infections or other complications among patients or healthcare workers merits an epidemiological investigation. The Infection Prevention and Control Director will notify the Infection Prevention and Control Chairman and the Administrator as soon as possible when an outbreak is suspected, and will lead the outbreak investigation. III. PROCEDURE I. STEPS A. Establish or verify the diagnosis of reported cases. 1. Develop specific criteria for definition of a case. Initially this may be a broad definition which is refined as the investigation proceeds (e.g., diarrhea in patients). 2. Write case definition. 3. Characterize the nature of disease; signs and symptoms (e.g., go to the patient s chart). 4. Obtain appropriate laboratory specimens to identify specific agent responsible. B. Confirm the existence of an outbreak. 1. Case finding: Use case definition to estimate the magnitude of the problem. 2. Compare current incidence with usual or baseline incidence (calculate rates, test if necessary). a. Observational methods Parametric methods (e.g., test). b. Nonparametric methods (e.g., Chi-square test, Fisher s exact test, Wilcoxin signed-rank test, Wilcoxin rank sum test, Man-Whitney test).

2 3. Assess the need for outside consultation report to public health authorities if required. 4. Institute appropriate early control measures based upon the magnitude and nature of the problem. 5. Confirm that specimens (e.g., sera) and isolates (e.g., epidemiologic markers) will be held until the investigator request or releases them. C. Seek additional cases of the disease. 1. Encourage immediate reporting of new cases. a. Laboratory reports b. Physicians c. Nursing staff d. Others as appropriate (e.g., radiology in cases of pneumonia). 2. Search for other cases that may have occurred retrospectively or concurrently. a. Laboratory results b. Medical records c. Patients records d. Physicians and nursing staff e. Public health data f. Other D. Characterize the cases of disease according to person, place and time. 1. Time a. What is the exact period of the outbreak? (Make sure to go back to the first case or first indication of outbreak activity). b. Given the diagnosis, what is the probable period of exposure? c. Record date of onset of illness for cases; draw an epidemic curve. d. Is the outbreak common source or propagated (continuing source, e.g., infections are transmitted from person to person in such a way that cases identified cannot be attributed to agent(s) transmitted from a single source)? 2. Place a. Provides clues to population at risk. b. Definition: service, nursing unit or patient care area, procedure room, etc. c. May involve use of tables or spot maps. d. May show clustering of cases. 3. Person a. Evaluation of patient characteristics (i.e., age, sex, underlying disease). b. Evaluation of possible exposures (i.e., procedures, nursing and medical staff, infected patients).

3 c. Evaluation of therapeutic modalities (i.e., invasive procedures, medication, antibiotics). 4. Calculate rates. E. Complete Quick and Dirty evaluation of outbreak. Complete A, B, C, and D. F. Formulate tentative hypothesis. 1. Record, tabulate and review data collected from above activities in order to summarize common host factors and exposures. 2. Based upon this analysis, (and literature review if necessary) develop a hypothesis (best guess) on the likely reservoir, source(s), and mode of transmission of the disease. In practice, the investigator may formulate several reasonable hypotheses, testing them simultaneously and acting upon the one which is most promising). 3. The hypothesis should explain the majority of cases frequently these will be concurrent cases not explained by the hypothesis that may be related to: a. Endemic or sporadic cases. b. A different disease (similar symptomatolgy). c. A different source or mode of transmission. G. Testing the hypothesis. 1. Many investigations do not reach this stage; investigation may end with descriptive epidemiology (problem goes away without interventions or does not require a special study). Whether or not an investigation, the hypothesis testing phase is a function of available personnel, severity of the problem and resource allocations. Examples of situations which should be studied include: a. Infection associated with a commercial product. b. Infection associated with considerable morbidity (e.g., bacteremia) and/or mortality. c. Infections associated with multiple services. 2. Epidemiologic approaches for testing a hypothesis. a. Case-control study (most frequently used). b. Cohort study. c. Prospective intervention study (experimental). 3. Other techniques or disciplines. a. Microbiology: Isolation and comparison of organisms from cases and controls. b. Other laboratory studies (e.g., toxicology may suggest etiology of disease if not infectious). 4. Analyze data derived from case investigation.

4 5. Demonstrate significant difference of incidence or exposure in contrasted population groups. 6. Refine hypothesis and carry out additional studies if necessary. H. Institute control measures. 1. May be done anywhere in process. 2. Identify specific preventive and control measures based upon nature of agent characteristic of high risk group and sources (i.e., eliminate contaminated product, modify nursing procedures, treat implicated carriers, immunize susceptibles, etc.) 3. Evaluate efficacy of control measures. a. Cases cease to occur, or return to endemic level. b. No change occurs (if so, return to F or re-evaluate cases). c. Use opportunity of an outbreak to review and correct other hospital practices related to the current situation which may contribute to an outbreak in the future. I. Write a report. 1. Introduction. a. Describing the circumstances leading to recognition of the problem. b. Background describing the setting in which the problem occurred. 2. Methods (description of the studies conducted). a. Methods (laboratory epidemiologic). b. Case definition, case-finding and verification of diagnosis. c. Sources of data. d. Hypothesis testing, if any. e. Description of type of study design; description of control group (s) and rationale for choice; statistical tests used. 3. Results a. Facts only; no explanations. b. May use tables, graphs and charts. c. Analysis of data and statistical conclusions (include p-values). 4. Discussion. a. Interpretation. b. Description of control measures. c. Description of other important outcomes, discoveries of new agents, reservoirs, modes of transmission, legal economic impact, etc. d. Recommendations for further surveillance and control.

5 5. References. 6. Disseminate report to: Chairman of Medical Executive Committee Administrator Infection Prevention and Control Committee