What are the criteria for tuberculosis close-contact screening?

TB Close Contact Screening Criteria

All contacts of persons with infectious tuberculosis should be prioritized into high, medium, or low categories based on exposure characteristics and individual susceptibility, with high-priority contacts (household members, children <5 years, immunocompromised persons, and those with prolonged close exposure) requiring immediate evaluation within 7 working days. 1

Priority Classification System

The screening criteria operate on a three-tier priority system that determines both who gets screened and how urgently:

High-Priority Contacts (Screen within 7 days)

These contacts require immediate evaluation regardless of symptoms:

• Household contacts - Anyone living in the same residence as the index patient
• Children aged <5 years - Due to higher risk of progression to severe/disseminated disease and shorter incubation periods 1
• Immunocompromised persons - Including HIV-positive individuals, those on immunosuppressive therapy, or with other conditions affecting immunity 1
• Close or prolonged exposure - Contacts spending extended time in small, poorly ventilated spaces with the index patient 1
• Congregate settings - Exposure in settings like shelters, correctional facilities, or healthcare facilities 1
• Contacts of highly contagious cases - Index patients with AFB smear-positive sputum, cavitary disease, or laryngeal TB 1

Medium-Priority Contacts (Screen within 14 days)

These contacts had less intense but still significant exposure and should receive tuberculin skin testing within 14 days of being listed 1.

Low-Priority Contacts

Contacts with limited exposure and low probability of infection. A single skin test at the end of the window period (8-10 weeks post-exposure) is preferred 1.

Screening Components

Initial Evaluation for All Priority Contacts

1. Tuberculin Skin Test (TST) at initial encounter

   • Positive threshold: ≥5 mm induration for any contact 1
   • This differs from other screening contexts where higher thresholds apply

2. Symptom assessment - Any TB-compatible symptoms warrant immediate evaluation regardless of test timing 1

3. Chest radiograph for:

   • All contacts with TST ≥5 mm 1
   • All high-priority contacts due to special susceptibility (children <5 years, immunocompromised) regardless of TST result 1
   • Any symptomatic contact immediately 1

Window Period Testing

Critical timing consideration: The window period between exposure and detectable TST reactivity is 8-10 weeks (not the previously recommended 10-15 weeks) 1.

• Initial negative TST obtained <8 weeks post-exposure is unreliable for excluding infection
• Repeat testing required at 8-10 weeks after last exposure for high and medium-priority contacts 1
• Exception: Low-priority contacts may receive single test at end of window period 1

Special Population Considerations

Children <5 Years (High Priority)

These children require the most aggressive approach:

• Full diagnostic evaluation including chest radiograph at initial encounter 1
• If initial TST <5 mm and exposure was <8 weeks ago: start window prophylaxis (presumptive treatment) after excluding active disease 1
• Repeat TST at 8-10 weeks post-exposure
• If second test negative: discontinue treatment
• If second test positive: complete full LTBI treatment course 1

Immunocompromised Contacts (High Priority)

• Similar evaluation protocol as children <5 years 1
• Even if TST remains negative at >8 weeks post-exposure, complete LTBI treatment is recommended after excluding active disease 1
• This reflects higher risk of progression despite negative testing

Index Patient Characteristics That Trigger Investigation

Highest priority for initiating contact investigation:

• AFB sputum smear-positive pulmonary TB 1
• Pulmonary cavities on imaging 1
• Laryngeal TB 1
• Prolonged infectious period (delayed diagnosis/treatment) 1
• Multidrug-resistant TB 1

Common Pitfalls to Avoid

1. Don't use two-step testing for contacts - This is for serial testing programs. A positive second test after initial negative should be classified as recent infection, not boosting 1

2. Don't wait for symptoms in high-priority groups - Children <5 years and immunocompromised contacts need chest radiographs regardless of symptoms or TST results 1

3. Don't dismiss early negative tests - Testing <8 weeks post-exposure cannot exclude infection; repeat testing is mandatory 1

4. Don't apply standard conversion criteria - The usual definition (10 mm increase over 2 years) doesn't apply here. Any change from negative to positive is significant in contact investigations 1

5. Don't overlook asymptomatic disease - Recent data shows significant proportions of TB cases among contacts are asymptomatic (37.5-66.7% in some cohorts) 2, emphasizing the importance of systematic screening beyond symptom inquiry

Expanding Investigations

Expand screening scope when:

• High transmission rates detected among initial high-priority contacts
• Secondary cases identified
• Outbreak situations with multiple linked cases 1
• Environmental factors suggest enhanced transmission (poor ventilation, prolonged exposure periods) 1

The evidence strongly supports risk-stratified screening rather than universal contact testing, as this optimizes resource allocation while capturing those at highest risk for infection and progression to disease 1, 3.