1. Legionnaires’ Disease Inter-professional Exercise Sept 11, 2018
Why we care about a Legionella outbreak &
answers to worksheet questions
Questions may be addressed to Dr. Shoham: Dr. Silva: or
Dr. Luke:

2. Nine Cases Confirmed In Northern Illinois
Nine Cases Confirmed In Northern Illinois
By News Services on July 20, 2018
POSTED IN LEGIONNAIRES' DISEASE, PUBLIC HEALTH
Nine residents of Illinois’ McHenry County were sickened with Legionnaires’ disease in less than a month, according to the McHenry County Department of Health, and officials are scrambling to identify if any “common denominators” exist between the individuals who were sickened.

3. http://www. chicagotribune
Lawsuit alleges state was negligent in veteran’s death after outbreak of Legionnaires’ disease
Chicago Tribune
July 20, 2018
The state of Illinois was negligent in its upkeep of a veterans home where outbreaks of Legionnaires’ disease that began in 2015 led to the deaths of residents, according to a lawsuit filed Thursday by the son of a man who died of the disease.

4. http://www. dph. illinois

5. Question 1: Would you call this an epidemic
Question 1: Would you call this an epidemic? Would you call this an outbreak?
Both epidemic and outbreak are usually defined as the occurrence of more cases in a place (or population) and time than expected. The rate of severe pneumonia observed in northern Illinois during the summer of 2018 is well above usual levels; above the "expected" or background rate of pneumonia in a community. The terms "outbreak" and "epidemic" are used interchangeably by many epidemiologists, although some consider the term “outbreak” to refer to a more localized situation, and “epidemic” to refer to a more widespread (and perhaps prolonged) situation.

6. Question 2: An outbreak investigation is initiated. Why?
Because the incidence of pneumonia is clearly above expected rates, people are dying from it and legionellosis is an illness that must be reported to the National Notifiable Diseases Surveillance System.
Question 4: List the potential causative/etiologic agents for a pneumonia of this severity. Focus on bacterial agents
Streptococcus pneumoniae, staphylococcus aureus, legionella pneumophilia, bacillus anthracis, haemophilus influenza, klebsiella pneumoniae, pseudomonas aeruginosa

7. Question 3: Review the steps of an outbreak investigation
Question 3: Review the steps of an outbreak investigation. Use the table below to describe how a health care and/or public health practitioner may be involved. Some boxes are filled to help you get started.
The steps in a field investigation include:
1. Establish the existence of an epidemic (or outbreak)
2. Verify the diagnosis
3. Establish criteria for case identification
4. Identify additional cases
5. Perform descriptive epidemiology: Orient the data according to person, place, and time
6. Develop and test hypothesis
7. Reconsider hypothesis
8. Perform additional studies if needed
9. Implement control measures
10. Communicate findings  

8. Health care
Public Health
1. Establish the existence of an epidemic (or outbreak)
e.g. Using surveillance data to detect epidemic
2. Verify the diagnosis
e.g. Laboratory tests
3. Establish criteria for case identification
4. Identify additional cases
5. Perform descriptive epidemiology: Orient the data according to person, place, and time
6. Develop and test hypothesis
7. Reconsider hypothesis
8. Perform additional studies if needed
9. Implement control measures
10. Communicate findings

9. Question 5: Which etiologic agent do you suspect may be the cause of this outbreak? Explain your reasoning.
Legionella pneumophilia. Severity, lack of person-to-person transmission, symptoms, case fatality rate

10. See initial line listing for variables collected.
Question 6: What information would it be important to collect from patients and family members? Group the information collected into categories. Remember to consider your chosen etiologic agent to help determine what data to collect.
See initial line listing for variables collected.
Case # Report Date Onset Date Alive Physician Diagnosis F C/NS C/S MA LC D N
V X-ray +/- Low Na+ Culture Age Sex Residence
Legend: F=fever; C/NS=cough no sputum; C/S=cough with sputum; MA=muscle aches; LC=loss of coordination; D=diarrhea, N=nausea; V=vomiting; N/A=not available
X-ray += radiologic evidence of pneumonia; - = no evidence; Low Na+= low plasma sodium levels; Culture=positive culture for etiologic agent
1=yes; 0=no

11. Question 7: What is a line listing
Question 7: What is a line listing? What is the value of presenting the data in this format?
A line listing is a table for which each column represents an important variable (e.g., name identification number, age, sex, exposures, etc.) while each row represents a different case, by number (as new cases are identified)
The value of a line listing is that it allows the investigator to scan key information on every case and update it easily.
Question 8: What is the value of an epidemic curve?
The value of an epidemic curve is to show the time course of an epidemic. It is drawn using a graph of the number of cases by their date of onset. This provides a visual display of the magnitude of the outbreak as well as a time trend.

12. Question 9: We have graphed the reported cases of pneumonia by estimated date of illness onset. What does this epidemic curve tell you?
That the cases have occurred throughout the summer with a significant increase over a few days in June, suggesting there may have been a large gathering at that time where multiple people were infected. That said, it is also clear that the risk was not confined to that time.
Question 10: Does the geographic spread, i.e., where the patients live, of the pneumonia cases tell you anything about the potential modes and/or source of transmission? Map the home towns of the patients on the map below.
With this outbreak, the geographic spread actually doesn’t provide much information as the cases occur throughout towns across northern Illinois and are not concentrated in any one community.

13. Question 11: Considering the etiologic agent your group has identified as the likeliest cause of this outbreak and its typical incubation period, what other types of information would you collect?
Did people attend any special event away from home where large number of people gathered? Had they traveled up to 2 weeks prior to onset of illness (considering the incubation time of your chosen etiologic agent)?
Question 12: Based on the additional data collected during follow-up discussions with the patients/families what do you think is/are the most likely site(s) where transmission of etiologic agent occurred?
Boylan Catholic High School 50th Class reunion

14. Question 13: Calculate the attack rate of the etiologic agent during the Boylan Catholic High School 50th Class reunion.
11 cases/65 total attendees /65 = 16.9%
Question 14: Use the online calculator ( to determine the 95% confidence interval for the attack rate associated with the etiologic agent that is the most likely cause of a proportion of the pneumonia outbreak observed in northern Illinois during the summer of 2018.
95% CI :

15. Question 15: Clearly the Boylan high school reunion is not the only source of infection for the cases identified during the summer of Based on additional information collected, what is the second most likely site of transmission?
Hotel in Alton, IL – a town outside of St. Louis
Question 17: With your knowledge of the route of transmission of this etiologic agent, what should be investigated at the locations identified?
Air conditioning, hot tubs, fountains – most common form of transmission of Legionella is contaminated aerosols produced by mists (air conditioning unites), water sprays or jets (hot tubs, fountains)

16. Question 17: What control measures would you suggest?
Identifying the source within each of the 2 venues (high school and hotel). Cleaning and/or dismantling the water supply to the source, replacing parts, if necessary. Retesting water associated with the source for several months after cleaning/dismantling.
Question 18: How did the efforts of the healthcare team members who cared for the affected patients and the members of the DuPage County Health Department complement each other in this outbreak investigation?
Think about the specialized training each team member brings to an investigation like this…