Assignment: Outbreak Investigation!

Evaluate an epidemiological outbreak.

Course outcome assessed/addressed in this Assignment:

 Evaluate an epidemiological outbreak.

Instructions

In this scenario you are working as an epidemiologist for the local health department. You received a call of a possible TB outbreak. You  have been assigned the case. Use the TB case (in Doc Sharing) to complete this possible outbreak investigation.

Question 1:

What questions should you ask and what information should you collect from the ICP while he/she is on the telephone with you? At this early juncture, should you consider initiating an investigation about these 2 cases?

The CDC classifies TB as a notifiable disease. "A notifiable disease is one for which regular, frequent, and timely information regarding individual cases is considered necessary for the prevention and control of the disease."3

Question 2:

At this point, would you consider this an outbreak?

You decide that the next step you should take is to visit the patients in the hospital, collect information from their medical records, and interview them.

Question 3: What should you have as goals in your interviews with these suspected TB cases?

Question 4: What types of questions should you ask the suspected cases?

Question 5: Complete the line list below for the confirmed cases.

Table 2. Line list for confirmed cases

Question 6:

Is this an outbreak? Provide your reasons.

Question 7:

What are the steps you should take in investigating this outbreak?

Question 8:

The purpose of this investigation is to identify any additional cases of TB and individuals who may have been infected by these cases. What is your "case definition" for transmission in this investigation? Remember a complete case definition should include information on person, place, time, and clinical characteristics.

The Tuberculin Skin Test (TST) may be used to determine if a person has TB infection. A TST is available at the health department or at a doctor's office. A health care worker injects a small amount of testing fluid (called tuberculin or PPD) just under the skin on the underside of the forearm. After 48 to 72 hours, the patient must return to have the skin test read by the health care worker. He/she may have a swelling-called induration-where the tuberculin was injected. The health care worker will measure this induration and explain to the patient whether the results are positive or negative. A positive reaction usually means that the patient has been infected with the TB bacteria. If a person has recently spent time with and been exposed to someone with active TB disease, his/her TST reaction may not yet be positive. He/she may need a second skin test 8 to 10 weeks after the last date of exposure to the TB patient because it can take several weeks after infection for the immune system to react to the TST. If a person's reaction to the second test is negative, he/she is considered not infected.10

Question 9:

At this point, who needs to be tested for transmission of TB, through a TST?

Question 10:

Are Cases 4 and 5 epidemiologically linked to the other cases? (Look at Table 3 above)

The suspected index case (Case 1) is a tenor in the 8 and 11a.m. church choirs. In the winter months, he was occasionally driven to church with Case 4, a tenor in the church choir. There were 5 different choir groups totaling approximately 300 to 500 members (per an outdated choir list). Aggregate and separate choir practices were held once a week in the church or in its basement with 3 separate choir groups singing together or in staggered time periods.

Choir groups were labeled as to the time the choir sang in church each Sunday (8 a.m. choir and 11 a.m. choir). Choir members' ages ranged from 5 to 70 years. The adult choirs rehearsed together once a week; on average, rehearsal time was 1 hour. Many choir members lived in other urban or suburban communities away from the church location. Commuting together usually was sporadic and ad hoc. The church and choir members were largely working, middle class African-Americans.

Part III. Analysis

Question 11:

Can you develop a hypothesis regarding this outbreak?

Only 300 of the assumed total of 500 choir members were accessible and available for tuberculin testing. Nonchoir church members were not tested. The entire church building including the stage and basement where all the choirs rehearsed was inspected for contributory factors (such as ventilation outlets) to environmental transmission.

Question 12:

What was the response/cooperation rate of the choir members, assuming there were 500 choir members? Why is this important?

It could not be ascertained for certain where transmission occurred, but the main church's choir loft, where most rehearsals occurred, was considered the most likely location for cases 1, 2, 3, and 5. Transmission to Case 4 could have occurred in the choir loft during joint practice or while commuting with Case 1. The basement, where some transmission could have occurred, had air conditioning units with 8 air outlets from a dropped ceiling. Air was re-circulated.

Of the 300 traced choir members tested, 120 belonged to the 11 a.m. choir; 25 members of the 120 11 a.m. choir members were TST reactors; 12 of the 25 reactors were tenors and 12 of 36 tenors were reactors.

Question 13:
Use the data from the 120 11 a.m. choir members who received TSTs to create a contingency table to look for an association between vocal range (as a proxy for location/exposure to the index case in the choir) and skin test result. Assume that the group has been assembled based on their exposure status and that level of exposure is stratified by vocal range (tenor vs nontenor) because the index case was a tenor. These 120 choir members received TSTs and when the data is available, populate this table.

Question 14:

What preventive measures would you recommend for those who had a positive TST, but did not have any other sign of disease?

Question 15:

Based on the pathogenicity-the ability of an agent to cause disease after infection, measured as the proportion of persons infected by an agent who then experience clinical disease-8 of TB, do you recommend future TSTs and studies?

Part V. Conclusion

Ten weeks after the initial tuberculin testing, 86 of the 11 a.m. nonreactor choir members were retested. Two new reactors (both tenors) were found and given treatment for latent TB infection. No additional cases were found. It should also be noted that the sopranos who sat directly in front of the tenors, separated by the floor air outlet-intake vents, did not have TB, and few sopranos had positive TST results.

Attachment:- tb_case_study.rar