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Guide to the Application of Genotyping to Tuberculosis Prevention
and Control
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Tuberculosis Genotyping Case Studies: How TB Programs
Have Used Genotyping
A Misdiagnosis that Was Identified with Genotyping
A 36-year-old woman came to the emergency room with a 2-day history
of fevers, cough, and right-sided pleuritic chest pain. She had
no known history of tuberculosis exposure. Her past medical history
was notable for injection drug use (heroin) up to the time of her
admission. Her physical examination showed a fever of 39ÂșC and signs
of consolidation at the right lung base. A chest radiograph showed
right lower lobe infiltrates with an associated small pleural effusion.
The patient was admitted to respiratory isolation and treated with
intravenous ceftriaxone. She responded quickly and became afebrile
after 2 days of therapy. A standard sputum culture grew normal oral
flora; blood culture results were negative. Three sputum specimens
were acid-fast bacilli (AFB) smear-negative, but she had a 15-mm
response to tuberculin skin testing (TST). A human immunodeficiency
virus (HIV) test was negative. She was discharged to complete 7
days of therapy with amoxicillin for community-acquired pneumonia.
She was called back to the TB Clinic 1 month after discharge when
one of the three sputum specimens grew drug-susceptible M. tuberculosis,
and she was given a diagnosis of tuberculosis. By that time she
reported feeling back to normal, and a repeat chest radiograph was
normal. Two additional sputum specimens were collected and were
AFB smear- and eventually culture-negative. She was treated with
isoniazid (INH), rifampin, pyrazinamide, and ethambutol for 2 months
and then with isoniazid and rifampin for 4 additional months. The
TB control program also performed a relatively large contact investigation.
Two years later, during a study in which all M. tuberculosis
isolates underwent genotyping, her isolate was found to match that
of a specimen from a laboratory proficiency test specimen that underwent
initial processing on the same day.
This case has several characteristic features of a false-positive
culture result. First, and most importantly, the clinical case was
atypical for tuberculosis with an acute onset and rapid resolution
with antibiotic therapy having no activity against mycobacteria.
Although the patient had latent tuberculosis (the positive tuberculin
skin test), the fact that the infiltrate completely resolved within
1 month, essentially without anti-tuberculosis therapy, is not consistent
with tuberculosis. Second, only one of several specimens grew M.
tuberculosis (a single-positive culture result). Routine review
of single-positive culture results is one method to detect potential
false-positive cultures. Treating this patient for TB required the
TB program to use valuable resources and exposed the patient to
the toxicity of unnecessary multidrug therapy.
Last Reviewed: 05/18/2008 Content Source: Division of Tuberculosis Elimination
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
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