Over the past two years, with our attention singularly focused on COVID-19, facility outbreaks with other pathogens have been particularly problematic. In a systematic review, Thoma et al (2022) identified 17 outbreaks of multidrug-resistant pathogens, most caused by Candida auris and carbapenem-resistant Acinetobacter baumannii (CRAB) with an overall mortality rate of 35%.1 With resources diverted to pandemic-related activities pathogens such as these and others have gone undetected. Additional contributing factors including staffing shortages and pandemic fatigue have led to breaches in standard infection prevention and control (IPC) practices.

Outbreaks are a serious threat to patient safety and can also damage a facility’s reputation. Management of outbreaks is costly and resource intensive. Because outbreaks are an infrequent occurrence in any given facility, it’s crucial that infection preventionists (IPs) understand how to promptly identify and control outbreaks.

 4 Simple Steps to Outbreak Management

The definitions for levels of disease, including outbreaks, are provided in Table 1. Ideally, we want to identify cases early before we have a full-blown outbreak on our hands.

Definitions for Levels of Disease
EndemicThe usual (baseline) prevalence of a pathogen in a given population within a geographic area (e.g., a usual flu season)
EpidemicA sudden increase above expected levels in the amount of disease in a population (e.g., more cases than is typically expected during the flu season)
OutbreakSame definition as epidemic, but is often used for a more limited geographic area such as a single healthcare facility
Pseudo-OutbreakThe recovery of the same organisms from cultures of patients who are not infected or colonized with the organism
ClusterAn aggregation of cases grouped in place and time that are suspected to be greater than the number expected (e.g., isolated to a single unit in a healthcare facility)
PandemicAn epidemic that has spread over several countries or continents, usually affecting a large number of people (e.g., Spanish Influenza, COVID-19)

Adapted from CDC’s Principles of Epidemiology in Public Health Practice (2012).2

Outbreaks are often first noticed by an astute clinician. Should such a clinician reach out to you, take the time to investigate. Sometimes the concern is unfounded or coincidental but too often it’s found to be valid. Also, trust your gut. If you are concerned over what you are seeing in your surveillance activities, then investigate. I recall a single day when I identified not one, but two patients who had respiratory isolates growing the same Penicillium species. Since the patients were on separate units, I took a wait-and-see approach. The next day, two additional patients were identified. Despite being a new IP, I knew this was a problem. But where does one start? Let’s take a look at the 4 key steps to managing an outbreak:

Step 1 — Verify the Existence of an Outbreak:

  • Are you seeing an uptick in cases? In my Penicillium example, I had never seen this pathogen before in my microbiology reports so my “spidey senses” were up. Ensure that the increase is not for reasons such as improvements in testing or changes in the population. This happened to me once when we improved our testing process for C. difficile. It’s also important to note that small numbers of cases or even a single case of an epidemiologically important pathogen such as C. auris, CRAB, or carbapenem-resistant Enterobacteriaceae (CRE) is cause for investigation.
  • Verify the diagnosis: This is critical. In my Penicillium example, after speaking with the patient’s physicians, I was able to learn that none of them exhibited signs or symptoms of fungal disease. The physicians were managing the cases as contaminants. My next thought was contaminated petri dishes, but after a visit to the hospital laboratory, this was ruled out.  
  • Look for commonalities among the patients. In my Penicillium example, I had four cases on two units, all on the same floor all of the hospital. Two of the patients were on a ventilator.
  • Summarize cases: Graph the number of cases by time (date). Much can be learned from analyzing frequency distributions using a histogram.

Step 2 — Develop a Case Definition:

A case definition is a set of objective and measurable criteria for deciding whether an individual should be classified as a case. It should be restricted by person, place, and time. A common mistake is to include the exposure or risk factors of interest. For example, in my Penicillium example, it was tempting initially to limit my definition to only patients on the units where positive patients resided. Consider having case definitions for confirmed, probable, and possible cases. As you gather more information, your definition may change. Note: no case definition is perfect – some mild cases may be excluded while others with similar symptoms but a different illness may be included. For an example of a case definition based on my Penicillium example, see Table 2.

Definition for the Penicillium Outbreak Example
Clinical criteriaAsymptomatic
Lab criteriaRespiratory specimen growing Penicillium spp.
PersonAll inpatients
PlaceAll inpatient units
TimeWithin the past 6 months
Case classification
Suspected: A case that meets the clinical criteria
Probable: A suspected case with signs and symptoms consistent with the disease and epidemiological link to a confirmed case
Confirmed: A suspected or probable case with lab confirmation

Adapted from CDC’s Principles of Epidemiology in Public Health Practice (2012).

Step 3 — Develop and Test Your Hypothesis:

The hypothesis is a proposed explanation for the outbreak made with limited evidence as a starting point for further investigation. It may address the source, transmission mode, and exposures of the pathogen. To test the hypothesis, compare it with the facts such as the clinical, laboratory, environmental, and/or epidemiologic evidence. In my Penicillium example, I hypothesized that the source of the pathogen was a flaw in the HVAC system. To test my hypothesis, I had the facility engineering staff inspect the HVAC duct servicing the effected floor. They found that the HEPA filter was too small for the HVAC duct. This allowed unfiltered outdoor air — where mold spores are ubiquitous — to enter the building. I further hypothesized that if the incorrect filter was replaced with the correct one, we should see no further isolates growing Penicillium. I was right. With the outbreak confirmed, I promptly notified my facility leadership. Also, since most state require reporting of outbreaks of any disease or the occurrence of any unusual disease, be sure to notify local public health authorities.

Step 4 — Implement Control Measures:

In my pseudo-outbreak example, placement of the correct HEPA filter immediately resolved the problem. I was very fortunate as most outbreaks do not resolve this simply and more often than not, the root cause is never identified.

Once you have identified the culprit and understanding its epidemiological traits such as reservoirs and mode of transmission, consider ways in which the chain of infection can be broken. Ensure compliance with basic IPC protocols such as hand hygiene and environmental cleaning and disinfection. Because many pathogens can persist in the environment for prolonged periods, environmental contamination can play a key role in outbreak management. For example, environment surfaces — particularly portable medical equipment — have been implicated in many of the C. auris outbreaks.3

 Key Take-Aways

Be sure to add this article as a tool for your IPC toolbox. Trust your gut — you likely know more than you think you do! Take the time to investigate concerns but always verify that there is indeed a problem. Graph the frequency distribution and develop a case definition. Test your hypothesis. Once you have confirmed the existence of an outbreak, promptly implement IPC measures. Last, be sure to document your outbreak “story” in a report for facility recording purposes.


1. Thoma R, Seneghini M, Seiffert SN, Vuichard G, Scanferla G, Haller S, et al. The challenge of preventing and containing outbreaks of multidrug-resistant organisms and Candida auris during the coronavirus disease 2019 pandemic: report of carbapenem-resistant Acinetobacter baumannii outbreak and a systematic review of the literature. Antimicrob Resist Infect Control. 2022 Jan 21;11(1):12.
2. Centers for Disease Control and Prevention. Principles of Epidemiology in Public Health Practice — Lesson 6: Investigating and Outbreak [Internet]. [Cited 2022 Feb 5, 2022]. Available from https://www.cdc.gov/csels/dsepd/ss1978/lesson6/section2.html#step11.
3. Centers for Disease Control and Prevention. Infection Prevention and Control for Candida auris [Internet]. [Cited 2022 Feb 5]. Available from https://www.cdc.gov/fungal/candida-auris/c-auris-infection-control.html.