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U.S. Department of Health and Human Services


Effective TB Interviewing for Contact Investigation: Facilitator Led Training Guide


10. Course Activities


Activity 4:  Infectious Period Exercise


  • To understand the considerations for determining infectiousness
  • To formulate an infectious period

Time Allotted

30 minutes total
  • 5 minutes for instructions and distributing exercises
  • 10 minutes of group work
  • 15-minute large group discussion of answers

Materials Needed

  • Easel
  • Markers
  • Copies of the “Infectious Period Exercise” on page 43 (one for each participant)

Pre-Course Procedure

The answers to this exercise will vary based on your health department’s guidelines for the calculation of an infectious period.  Therefore, no answers are provided to these questions.  Copy the exercise on page 43 and hand a copy to each participant. 


  1. Ask the participants how to calculate the infectious period for their area.  This should include a. beginning date, b. end date, c. criteria for onset of symptoms.
  2. Ask the participants to work for about 10 minutes individually to calculate the infectious period for each example.
  3. After 10 minutes, ask for volunteers to share with the class the infectious period for each example. Whether correct or incorrect, ask the participant the way in which this period was calculated for each example.  Correct any incorrect answers.
  4. The participant should draw a diagram to visually explain how the infectious period was calculated.  The diagram should look like Figure 7 with included dates as the answers.
Figure 7. Diagram of infectious period

Infectious Period, Number of months back, Beginning of infectious period, Onset of symptoms OR Beginning of treatment, if asymptomatic, 3 negative sputum smears


5. Answer any questions that may arise.  Be prepared to answer questions on topics such as

  • Having multiple infectious periods for the same patient;
  • Criteria for ending the infectious period;
  • Varying an infectious period in the context of each contact such as if the patient did not have contact with a close contact at some point before being hospitalized for infectious TB, i.e., the infectious period can end when contact is broken; and
  • Formulating the infectious period without the presence of cough or any TB symptoms.


The infectious period brings focus to the TB interview process.  Here is a quick review of the formulation of the infectious period.  This is the time frame during which potential exposure to others may have occurred while the patient was infectious or able to transmit TB.  Often, the beginning of the infectious period is the date of the onset of symptoms, especially coughing.  Local or state standards should be used to determine the beginning of the infectious period.  Some health department guidelines denote a specified period prior to the patient’s recollection of the onset of symptoms, particularly cough. 

For the purpose of the contact investigation, the end of the infectious period is determined by all of the following criteria:

  • Symptoms, such as frequency and intensity of cough, have improved
  • Patient has been receiving adequate treatment for at least 2 weeks
  • Patient has shown some evidence of a bacteriological response, such as the reduction of the grade of the AFB sputum smear or conversion to negative sputum smears.


  • Exposure to contacts has ended

The infectious period should be stated in the form of start date to end date.  The infectious period provides a timeframe for the patient when identifying information on contacts.



Activity 4:  Infectious Period Exercise

Participant Handout


Calculate the infectious period for the following cases.  It should include start and end dates. Base your answers on your health department’s standards for calculating an infectious period.  Be prepared to discuss with the class how you came up with your answer.  You can use a diagram like the one below to calculate the infectious period.


Infectious Period, Number of months back, Beginning of infectious period, Onset of symptoms OR Beginning of treatment, if asymptomatic, 3 negative sputum smears

  1. Joe was hospitalized on June 6 and started TB treatment that day.  He claimed he had been coughing since April 20.  He had three consecutive negative smear results as of July 10 and had improved symptoms.  What is the infectious period?
  2. Philip was hospitalized on December 4 with symptoms of fever, night sweats, and cough.  He was diagnosed with TB on December 10 and started on TB treatment that day.  Philip states that he started coughing around November 6.  His symptoms resolved on January 27.  Three consecutive sputum smears were not negative until February 10.  What is the infectious period?
  3. Mary complained that she had been coughing since March 10.  She started TB treatment on May 24.  Mary left the hospital against medical advice on June 7 but was readmitted on July 8.  She had three consecutive negative smears as of August 1, during the second hospitalization.  What is the infectious period?
  4. David was diagnosed with TB on February 10, based on skin test and chest X-ray results.  He was asymptomatic and treated on an outpatient basis.  His sputum smears were negative prior to treatment but sputum culture was identified as M. tuberculosis.  His treatment ended on August 5.  What is the infectious period?
  5. Carla was diagnosed with TB disease and had night sweats, fever, and weight loss when admitted to the hospital on May 19.  She claims her symptoms began around April 3.  She denies ever having had a cough.  Carla was admitted into the hospital and three consecutive induced sputum smears were negative on June 21. What is the infectious period?


Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination -

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