Summary of respiratory outbreak investigation strategies
For more information, please read the full Respiratory Disease Outbreak Investigation Guidance (pdf).
Step 1. Determine if an investigation is warranted
Potential triggers for investigation include (but aren't limited to):
- Evidence of severe illness (two or more deaths, or hospitalizations involving 3 or more individuals or 0.2% or more of a cohort >1,500 individuals, whichever is larger) within a 2-week period in an institutional cohort.*
- Chest x-ray-confirmed pneumonia in 3 or more epidemiologically linked individuals, especially if the etiology is unknown.
- Unusually high morbidity in an institutional cohort* manifested by prolonged (3 or more days) and frequent absenteeism (10 or more individuals or 20% or more of individuals, whichever is larger).
- Institutional outbreaks of influenza-like illness (documented fever 100º F or greater with cough or sore throat) in settings involving a population at increased risk for severe complications from flu (long-term care facilities, medical group homes, or a neonatal intensive care unit or oncology unit).
- Outbreaks of vaccine-preventable diseases.
When these findings are present please contact the PHD epidemiologist on call (971-673-1111) within 24 hours of receiving a report of a possible outbreak. PHD epidemiologists are also glad to discuss respiratory outbreaks that don't meet these criteria and can assist with planning and investigating respiratory outbreaks.
*An institutional cohort is defined as the employees, students, or residents of a worksite, school, or a permanent or temporary congregate living setting such as a long-term care facility, jail, or camp.
Step 2. Determine cause and course of the outbreak
Collect basic information about symptom profile and who is affected.
- For the ill persons that you are aware of when first notified about the outbreak, use the Respiratory Symptom Log (Line List) as a PDF or Excel spreadsheet to develop a line list with demographics, symptom profile and onset, and pertinent health care info (hospitalization, chest X-ray findings, etc.). This helps characterize the outbreak in terms of who is at risk. That information, coupled with the system profile, can often provide early clues as to what pathogen might be causing the outbreak. Getting solid information about dates of onset gives you the information you need to make an epidemic curve.
- Develop a case definition. Include symptoms, timeframe for onset, and place of exposure, if relevant.
- Create an epidemic curve to track the course of the outbreak.
- With Public Health Division epidemiologist who is on-call, develop plan for specimen collection and testing:
In some cases, e.g., environmental exposures to Legionella or Psittacosis, it may be useful to develop a questionnaire in collaboration with PHD epi.
Step 3. Implement control measures
For outbreaks involving confirmed or strongly suspected communicable respiratory infections:
- Provide basic information about the benefits of hand hygiene
- Recommend ready access to sinks with soap and warm water and alcohol-based hand sanitizer
- Review benefits of cough etiquette and share location of "Cover Your Cough (pdf)" posters
- Share benefits of having ill persons stay home until asymptomatic for 24 hrs or with some infections, such as pertussis and active tuberculosis, until they have been on effective medication long enough that they are no longer infectious
- Recommend isolation of ill persons until they can go home
- Explain benefits of age-appropriate immunization in settings of vaccine-preventable disease
- Consider immunization clinics if illness is vaccine preventable and many at high risk of complications are involved
- Target prophylaxis efforts for outbreaks involving pathogens that put certain groups at increased risk of severe disease (e.g. influenza in transplant units, pertussis in daycare settings, etc.)
- Closure of an institution may be considered if needed for environmental cleaning or if widespread absenteeism prevents effective functioning of a school or workplace. Closures are typically the decision of the facility and ideally are made in consultation with public health.
Step 4. Document control of outbreak
You probably don't need to continue with your line list after your initial assessment. As you monitor the outbreak though, it's very useful to get a tally of how many people present each day with new onset illness that is consistent with your case definition. Then you can regularly update an epidemic curve to see if number of new cases is decreasing and illness has returned to baseline. For uncommon conditions, this might be when two incubation periods have elapsed with no new cases.
Step 5. Managing special situations
Outbreaks in long-term care facilities (LTCF)
Outbreaks in schools or workplaces