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Self-Study Modules for Effective TB Interviewing

The TB interview

Infectious Period

In order to bring focus to the interview process, the infectious period must be determined.† This period is a time frame in 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 when the onset of symptoms occurs, 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 recollection of the onset of symptoms, particularly coughing.†

For the purpose of the contact investigation, the end of the infectious period is determined by the existence of 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 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.

The determination of the infectious period is based on several factors and should result from a collection of all relevant information from both the patient and the patientís medical record.† The infectious period may exceed 6 months; however, the patientís memory of details beyond that time frame may be unreliable.† Regardless, if review of the patientís medical record or other source indicates that the patient has had signs and symptoms of pulmonary or laryngeal TB for more than 6 months, collection of contact and congregate setting information prior to that time should be done.† Using a retrospective timeline, the results of contact evaluations will help determine when to stop identifying more contacts. This timeline should start with the date of the interview and work its way back in time.†

A patient will most likely not be able to provide you with exact onset dates for symptoms.† Asking the patient to associate symptoms with events may assist.† For example, a patient can be asked if he or she remembers coughing around a major event or holiday (e.g., his or her birthday, Christmas).

In a source case investigation for a child, the infectious period generally begins 3 months prior to the date of the interview.† The infectious period end date is the interview date.† The factors regarding treatment and sputum conversion for ending the infectious period in source case investigations do not apply because most young children, as well as persons with latent TB infection, are not usually infectious.



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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