4 Outbreak management Flashcards
What is definition of an outbreak?
An outbreak of infection or food-borne illness may be defined as two or more linked cases of the same illness or the situation where the observed number of cases exceeds the expected number, or a single case of disease caused by a significant pathogen (e.g. diphtheria or viral haemorrhagic fever).
It is can also be defined as the occurrence of disease at a rate greater than that expected within a specific geographical area and over a defined period of time (Beck-Sague et al., 1997 )
What are the initial major steps if an outbreak is suspected?
Inform - notify IPC of potential outbreak
Isolate any potential cases to prevent further spread
Implement appropriate infection control measures to break chain of infection
What is the general meaning of these terms when defining cases?
Confirmed cases
Probable cases
Possible cases
1) confirmed case - when the patients have clinical signs and symptoms of the disease and the diagnosis
is confirmed by laboratory analysis of the appropriate specimen(s)
2) probable case - when the patients have clinical signs and symptoms of the disease or are epidemiologically
linked (been exposed to a confirmed case, eaten the same food, stayed in the same hotel, etc.) to a confirmed case
3) possible case - when the patients have clinical signs and symptoms without being a confirmed or probable case.
Once an outbreak is suspected, the first step is to confirm a true outbreak
What are potential causes of a pseudo-outbreak?
Laboratory
Ward
Environment
Laboratory factors
◆ Introduction of new test which was previously unavailable locally.
◆ Improved laboratory techniques for identification.
◆ Introduction of new laboratory test with poor specificity and/or sensitivity.
◆ Contamination during processing in the laboratory, e.g. due to contamination of
media or cross contamination of specimen during processing.
Ward level
◆ Incorrect diagnosis of clinical entity.
◆ Mislabelling of specimens. Remember, if in doubt ask for a repeat specimen!
◆ Contamination during collection if the correct procedure for collection of specimens
is not followed. Please refer to local guidelines for collection of specimens.
◆ Failure to distinguish community-versus hospital-acquired infection.
Environmental factors
◆ Use of water of poor microbiological quality in the washer disinfectors used for
decontamination has been responsible for pseudo-outbreaks. Misdiagnosis of
tuberculosis has been reported due to contamination of the endoscope with environmental mycobacteria (e.g. Mycobacterium chelonae ) from the rinse water which
subsequently contaminated bronchial washings sent for culture.
◆ Tap water contains microbes including Mycobacterium spp. If tap water is used by
the microbiology laboratory to perform a Ziehl–Neelsen (ZN) stain, it can give a
false positive diagnosis for tuberculosis.
Epidemic curves can be plotted to give vital information during an outbreak.
What information can be gathered?
◆ Determine whether the source of infection was common or continuous or both.
◆ Identity the probable time of exposure of the cases to the source(s) of infection.
◆ Identity the probable incubation period.
◆ Determine if the problem is ongoing or not.
What are definitions of these epidemic curves?
Point source
Point source : in a point source outbreak all cases have the same origin, i.e. index case/same person or a single vehicle which has been identified as the primary reservoir or means of transmission. For example, if there is an abrupt increase in the number of cases over a short time period, the curve suggests single exposure to a point source of contamination. It is important to note that in an outbreak situation, sometimes it may be possible that when an extended case finding is carried out, an index case may not be the primary case but the case who has been either not noticed or not reported initially or has been discharged from the health care facility
What are definitions of these epidemic curves?
Continuous
Intermittent
Continuous source : in a continuous source outbreak, the infections are transmitted from a reservoir and cases occur over a longer period (Figure 4.2 ). Epidemics can occur due to person-to-person transmission, from the environment, or from contaminated food or water. To determine the probable period of exposure of cases in a continuous source outbreak it is necessary to know the specific disease involved, dates of onset of cases, and either mean or median, or minimum and maximum, incubation period(s) for the specific disease.
It is important to note that exposure may be continuous or intermittent; if the exposure is intermittent then the curve will have irregularly spaced peaks.
What are definitions of these epidemic curves?
Propagated
Propagated source – does not have a common source but instead caused by spread of pathogen from one susceptible person to another; transmission may occur directly (person-to-person) or via an intermediate host; tends to have a series of irregular peaks reflecting the number of generations of infection; multiple peaks separated by approx. one incubation period; e.g., person-to-person spread of shigellosis
What are the steps of investigating an outbreak?
Confirm existance of outbreak - confirm diagnosis with testing
Create a case definition - can be broad to start with
Construct an epidemic curve
Develop and test the hypothesis - case-control or retrospective cohort study
Implement control measures
Write an outbreak report
What is the importance of an end of outbreak report?
◆ Review the experience of all participants involved in the management of the
outbreak.
◆ Identify any shortfalls and particular difficulties that were encountered.
◆ Revise the outbreak control plan in view of the current experience.
◆ Recommend, if necessary, structural or procedural improvements which would
reduce the chances of recurrence.
◆ Write the final outbreak report with recommendations outlining action needed to
be taken with timeline to prevent it recurrence.
What is a look-back investigation, and when might it be performed?
Look-back investigations refer to the process of identifying, tracing, recalling, counselling, and testing patients or HCWs who may have been exposed to an infection. An example is the case of a HCW who has undertaken exposure-prone procedures on surgical patients and is later found to be positive for a blood-borne virus (e.g. HIV,
hepatitis B or C virus) or a HCW who has been diagnosed with open pulmonary tuberculosis and has been working in the health care facility in a clinical area especially with susceptible patients.
A similar process may be needed if there is a breakdown and failure in the normal processes of disinfection or sterilization of instruments (e.g. failure to adequately disinfect/sterilize endoscopes or items/equipment which may have put patients at risk from infection)
Failure of sterilisation of a device. You decide to perform a look-back investigation
What steps are involed?
◆ Confirm disinfection or sterilization reprocessing failure.
◆ Impound any improperly disinfected/sterilized items.
◆ Do not use the questionable disinfection/sterilization unit (e.g. sterilizer, automated
endoscope reprocessor) until proper functioning can be assured.
◆ Inform key stakeholders.
◆ Conduct a complete and thorough evaluation of the cause of the disinfection/
sterilization failure.
◆ Prepare a line listing of potentially exposed patients.
◆ Assess whether disinfection/sterilization failure increases patient risk for infection.
◆ Inform expanded list of stakeholders of the reprocessing issue.
◆ Develop a hypothesis for the disinfection/sterilization failure and initiate corrective
action.
◆ Develop a method to assess potential adverse patient events.
◆ Consider notification of local and national authorities.
◆ Consider patient notification.
◆ Develop long-term follow-up plan.
◆ Perform after-action report.
