What is the appropriate diagnostic and therapeutic approach for a patient with a 7‑day cough, evening chills, and a positive Mantoux (tuberculin skin) test?

Diagnostic and Therapeutic Approach for Cough with Evening Chills and Positive Mantoux

Your patient requires immediate chest radiography and sputum collection for acid-fast bacilli smear and culture to rule out active pulmonary tuberculosis, because a positive Mantoux test cannot distinguish between latent infection and active disease, and the presence of symptoms (7-day cough and evening chills) raises significant concern for active TB. 1

Immediate Diagnostic Workup

Obtain the following tests urgently:

• Chest radiograph – mandatory next step for all patients with positive tuberculin test and respiratory symptoms to differentiate active disease from latent infection 1, 2, 3

• Three sputum specimens collected on separate days for:

  • Acid-fast bacilli (AFB) smear 1
  • Mycobacterial culture on both liquid and solid media 1, 4
  • Drug susceptibility testing 1

• Medical history focusing on:

  • Duration and character of cough (productive vs. non-productive) 1
  • Presence of fever, night sweats, weight loss, anorexia, hemoptysis 1, 3
  • HIV risk factors and immunosuppression status 1
  • Previous TB exposure or treatment 1, 5

Clinical Context: Why Symptoms Matter

The combination of cough ≥7 days plus evening chills (constitutional symptoms) in a Mantoux-positive patient creates high suspicion for active TB rather than latent infection. 1 While guidelines typically define "prolonged cough" as >2-3 weeks for TB suspicion 1, 6, your patient's positive Mantoux combined with any respiratory symptoms warrants immediate evaluation because:

• Pulmonary TB should be suspected in persons with productive, prolonged cough (>2 weeks duration) plus fever, chills, night sweats, or other constitutional symptoms 1, 3
• A positive tuberculin test with symptoms requires exclusion of active disease before considering latent TB infection treatment 1, 2
• Culture-positive pulmonary TB can present with cough as short as 1 month, especially when accompanied by fever 5

Interpretation of Positive Mantoux Test

A positive Mantoux test indicates TB infection but does NOT differentiate between:

• Active pulmonary disease
• Latent TB infection (LTBI)
• Previously treated TB 2

Key points about tuberculin testing in this context:

• The test remains positive for life after TB infection, regardless of treatment status 2
• Sensitivity in active pulmonary TB is approximately 93% when induration is 10-19mm 7
• A positive test supports the diagnosis but requires chest radiography and sputum studies to determine disease activity 1, 2

Treatment Decision Algorithm

If Active TB is Confirmed (positive AFB smear or culture with compatible chest radiograph):

Initiate four-drug therapy immediately: 1, 8

• Isoniazid + Rifampin + Pyrazinamide + Ethambutol for 2 months (intensive phase) 1, 8
• Followed by Isoniazid + Rifampin for 4 months (continuation phase) 1, 8
• Ethambutol can be discontinued once drug susceptibility confirms no resistance 1, 8

Report the case to your local health department immediately to initiate contact investigation 1

If Active TB is Excluded (negative sputum studies, normal or stable chest radiograph, symptoms resolve):

Consider treatment for latent TB infection: 1, 2

• Preferred regimen: Isoniazid + Rifapentine weekly for 3 months, OR Isoniazid + Rifampin daily for 3-4 months 1, 9
• Alternative: Isoniazid alone for 9 months (especially in children) 1, 9
• Do NOT treat for LTBI if the patient has already completed a full course of TB treatment in the past – persistent Mantoux positivity after completed therapy is expected and does not indicate treatment failure 2

Critical Pitfalls to Avoid

Do not delay sputum collection and chest radiography – a positive Mantoux test alone cannot rule in or rule out active disease, and symptomatic patients require microbiologic confirmation 1, 2, 5

Do not rely on the Mantoux test to exclude TB – approximately 7-12% of patients with active TB may have negative or weakly positive tuberculin tests, especially if immunosuppressed 1, 4

Do not start LTBI treatment without excluding active disease first – treating active TB with single-drug or two-drug LTBI regimens will lead to drug resistance 1, 8

Do not assume a normal chest radiograph excludes TB – culture-positive pulmonary TB with normal chest radiography occurs in up to 10% of cases, particularly in patients with cough >1 month, fever >1 week, or recent TB exposure 5

Special Considerations

If HIV-infected or immunosuppressed:

• Use a 5mm induration cutoff for Mantoux positivity 1
• Assess clinical and bacteriologic response closely, as treatment may need prolongation 8
• Consider anergy – negative Mantoux does not exclude TB in this population 4, 3

If sputum cannot be obtained or remains negative despite high clinical suspicion:

• Proceed to bronchoscopy with bronchial brushings and transbronchial biopsy (diagnostic yield 27-78%) 4
• Collect post-bronchoscopy sputum specimens (yield up to 80% in HIV-infected patients) 4