Lesson
Separate Infection, Disease, and Transmission
M. tuberculosis can persist under immune containment or produce pulmonary, laryngeal, disseminated, and organ-specific disease. Infectiousness depends on site, aerosol generation, burden, ventilation, duration, and treatment response.
- Latent infection
- Active disease
- Granuloma
- Aerosol
- Reactivation
Inhaled particles reach the distal respiratory tract.
Cell-mediated immunity can establish latent infection.
Loss of containment creates tissue injury and symptoms.
Aerosol generation can expose the next person.
Distinguish containment from eradication
Latent TB infection is asymptomatic and not contagious, but viable bacilli can persist. A future immune deficit can convert containment into active disease.
Recognize pulmonary disease
Cough, hemoptysis, fever, night sweats, weight loss, fatigue, and compatible imaging raise concern. Extrapulmonary disease can involve lymph nodes, pleura, bone, kidney, brain, and other sites.
Trace the aerosol pathway
Pulmonary or laryngeal disease can release small airborne particles during coughing, speaking, singing, or aerosol-generating procedures. Droplet precautions alone do not address this pathway.
Let host biology change urgency
Recent infection, HIV, transplant, TNF inhibition, substantial corticosteroid exposure, cancer therapy, kidney disease, diabetes, and very young age can increase progression risk.
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Lesson
Use Infection Tests Only When the Result Can Lead Somewhere
TST and IGRA detect immune sensitization to M. tuberculosis antigens. They do not determine whether active disease is present and can be falsely negative in disease or immune compromise.
- Targeted testing
- IGRA
- TST
- Induration
- False negative
Test when exposure or progression risk makes treatment useful.
BCG, return ability, age, immunity, and access shape the choice.
TST induration thresholds change with clinical risk.
Symptoms and imaging come before preventive treatment.
Select IGRA deliberately
IGRA is preferred in people who received BCG and in those unlikely to return for TST reading. It requires one visit but depends on proper blood handling and timely laboratory processing.
Read TST correctly
Measure transverse induration, not redness, at 48 to 72 hours. A threshold of at least 5 mm applies to the highest-risk groups, at least 10 mm to defined exposure or clinical-risk groups, and at least 15 mm to people with no known risk.
Respect the negative boundary
A negative infection test does not exclude active TB in a symptomatic patient, recent contact in the window period, or person with impaired immunity.
Plan the positive result before testing
A positive test requires symptom assessment and chest imaging, plus microbiology when disease is possible. LTBI treatment begins only after active disease has been excluded.
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Lesson
Confirm Disease Without Delaying Control
Presumed pulmonary TB requires simultaneous airborne protection, microbiologic confirmation, resistance detection, public-health notification, and assessment of competing diagnoses.
- Airborne isolation
- Three specimens
- AFB smear
- NAA
- Culture and susceptibility
Contain exposure while disease is still presumed.
Estimate burden and identify MTB rapidly.
Grow the organism and define susceptibility.
Report early and activate contact and treatment systems.
Collect a complete respiratory series
Obtain at least three consecutive sputum specimens 8 to 24 hours apart, with at least one early-morning specimen. Collect in an airborne infection isolation room, sputum booth, or another controlled ventilated setting.
Keep smear in its lane
AFB smear is rapid and can estimate organism burden, but it is neither specific for M. tuberculosis nor sensitive enough to exclude disease.
Use NAA for speed
Perform NAA on at least one respiratory specimen when the result can change therapy or TB-control action. A rifampin-resistance signal demands immediate molecular resistance work and expert consultation.
Preserve culture and susceptibility
Culture remains the laboratory confirmation foundation. Molecular and growth-based susceptibility answer complementary resistance questions.
Report presumed disease promptly
Active or presumed TB disease is reportable in every state. Engage the local or state health department before final culture so isolation, contacts, laboratories, and treatment support can begin.
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Lesson
Choose the Shortest Safe Preventive Pathway
CDC preferentially recommends short-course rifamycin-based LTBI treatment because it is effective and more likely to be completed. The source isolate, interactions, pregnancy, HIV therapy, organs, and adherence determine the best regimen.
- 3HP
- 4R
- 3HR
- 6H
- 9H
Twelve doses of isoniazid and rifapentine for eligible patients.
One hundred twenty rifampin doses with interaction ownership.
Ninety daily isoniazid and rifampin doses.
Longer isoniazid when rifamycin pathways do not fit.
Use 3HP in eligible patients
Give isoniazid plus rifapentine once weekly for 12 doses over three months. Adult and adolescent isoniazid is 15 mg/kg, maximum 900 mg. Rifapentine is weight based to 900 mg. Do not use during pregnancy or anticipated pregnancy.
Use 4R when rifampin fits
Give rifampin 10 mg/kg, maximum 600 mg, daily for 120 doses over four months in adults. Confirm source susceptibility and manage induction before prescribing.
Use 3HR as a combined short course
Give adult isoniazid 5 mg/kg, maximum 300 mg, plus rifampin 10 mg/kg, maximum 600 mg, daily for 90 doses over three months.
Reserve longer isoniazid alternatives
Daily isoniazid 5 mg/kg, maximum 300 mg, for 180 doses over six months or 270 doses over nine months is an alternative when preferred rifamycin regimens cannot be used.
Add pyridoxine where it matters
Use pyridoxine 25 to 50 mg daily with isoniazid during pregnancy and in people at increased neuropathy risk, including diabetes, HIV, kidney failure, alcohol use, malnutrition, and older age.
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Lesson
Connect Each Drug to Its Necessary Work and Its Harm
The regimen succeeds because multiple drugs reach different bacterial populations and prevent resistance. Each contribution comes with a distinct mechanism, exposure requirement, and toxicity signature.
- Isoniazid
- Rifamycins
- Pyrazinamide
- Ethambutol
- Moxifloxacin
Block mycolic-acid synthesis and protect nerves with pyridoxine when indicated.
Block RNA polymerase while managing potent induction.
Reach acidic populations while monitoring liver and urate effects.
Suppress resistance until susceptibility clarifies the regimen.
Use isoniazid with pyridoxine awareness
KatG activates isoniazid, which disrupts mycolic-acid synthesis. Common adult daily dosing is 5 mg/kg, maximum 300 mg. Watch hepatic injury, neuropathy, seizures, and increased phenytoin exposure.
Treat rifamycins as system-level drugs
Rifampin and rifapentine inhibit bacterial RNA polymerase. Rifampin is commonly 10 mg/kg, maximum 600 mg daily. Orange secretions are expected, but broad enzyme and transporter induction can destabilize essential co-therapies.
Use pyrazinamide for sterilizing activity
Pyrazinamide contributes in acidic intracellular environments and supports treatment shortening. Dose by current weight and kidney function. Monitor hepatic injury and symptomatic hyperuricemia or gout.
Use ethambutol as susceptibility protection
Ethambutol inhibits arabinosyl transferases. Common adult daily dosing is 15 to 20 mg/kg. Document vision and adjust interval in kidney impairment. Stop and evaluate new acuity or red-green discrimination change.
Use moxifloxacin only inside the studied pathway
Moxifloxacin 400 mg daily is part of the eligible four-month HPZM regimen. Review QT, electrolytes, tendon, neuropathy, dysglycemia, central nervous system effects, and polyvalent-cation timing.
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Lesson
Select a Regimen That Matches the Evidence, Not Merely the Calendar
Current U.S. guidance supports an eligible four-month rifapentine and moxifloxacin regimen, the established six-month HRZE and HR regimen, and a shortened pediatric pathway for defined nonsevere disease.
- 2HPZM/2HPM
- 2HRZE/4HR
- Eligibility
- Dose count
- Pediatric nonsevere TB
Rapid and growth-based evidence supports the pathway.
Age, weight, site, pregnancy, QT, and interactions control shortening.
Use HPZM then HPM or HRZE then HR without improvising.
Completion depends on delivered doses and response.
Use the standard six-month frame
Give two months of isoniazid, rifampin, pyrazinamide, and ethambutol, followed by four months of isoniazid and rifampin when susceptibility and response support it.
Use the four-month adult and adolescent pathway precisely
For eligible people age 12 or older and at least 40 kg, give 56 daily doses of rifapentine 1,200 mg, moxifloxacin 400 mg, isoniazid 300 mg, and weight-based pyrazinamide, followed by 63 daily doses of rifapentine, moxifloxacin, and isoniazid. The complete course contains 119 daily doses. Give with food and pyridoxine 25 to 50 mg daily.
Keep the exclusion boundary visible
The four-month HPZM pathway was not studied for age under 12, weight under 40 kg, pregnancy, breastfeeding, most extrapulmonary disease, relevant resistance, major QT risk, or clinically important drug interactions.
Extend the standard continuation phase selectively
A seven-month continuation phase can be required when cavitation and a positive two-month culture coexist or when pyrazinamide was omitted.
Use the pediatric recommendation only for nonsevere disease
Children and adolescents age 3 months through 16 years with defined nonsevere presumed drug-susceptible TB can receive two months of HRZ with or without E followed by two months of HR. Severe, miliary, obstructive, cavitary, and important extrapulmonary disease require another pathway.
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Lesson
Build Monitoring Around Decisions
A monthly visit is the minimum clinical frame, not the maximum monitoring plan. Baseline risk, regimen, symptoms, laboratory results, exposure, and public-health needs determine what must be measured more often.
- Baseline
- Monthly assessment
- Hepatic injury
- Vision
- Neuropathy
Record organs, vision, nerves, weight, drugs, and microbiology.
Reconcile symptoms, doses, barriers, interactions, and response.
Act on hepatic, visual, neurologic, cardiac, or hematologic injury.
Preserve enough active therapy with expert guidance.
Create an interpretable baseline
Map disease sites, weight, medication list, liver and kidney risk, HIV, pregnancy and lactation context, neuropathy, vision, QT risk, blood counts when relevant, susceptibility, and social barriers.
Perform monthly clinical monitoring
Reconcile every dose, missed-dose pattern, symptom, weight, new medication, interaction, adverse effect, access barrier, and response marker at least monthly.
Respond to hepatic warning symptoms
Anorexia, nausea, vomiting, abdominal pain, dark urine, or jaundice during hepatotoxic therapy requires prompt evaluation. Clinically significant suspected injury can require holding hepatotoxic drugs and expert-guided reconstruction.
Act on visual and neurologic change
New visual loss, red-green difficulty, progressive numbness, weakness, gait change, or linezolid-related blood-count abnormality requires immediate assessment rather than waiting for routine follow-up.
Use microbiology as a response measure
Obtain monthly sputum smear and culture in the four-month HPZM pathway until two consecutive cultures are negative. Persistent positivity triggers adherence, exposure, resistance, and disease reassessment.
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Lesson
Design Around the Whole Person
Rifamycin induction, HIV therapy, pregnancy, lactation, kidney disease, liver disease, and interacting medicines can alter the safest effective regimen. These are design variables, not afterthoughts.
- Rifamycin induction
- HIV
- Pregnancy
- Lactation
- Organ disease
Protect anticoagulation, contraception, ART, transplant drugs, and methadone.
Use CD4 and disease site to coordinate ART initiation.
Treat active disease promptly and use current narrative risk.
Preserve regimen activity while adjusting exposure and monitoring.
Manage induction as a clinical system
Rifampin and rifapentine can lower exposure to anticoagulants, hormonal contraception, methadone, antiretrovirals, transplant drugs, antiseizure medicines, and many other agents. Assign an alternative or monitoring plan to every important interaction.
Coordinate ART timing
For untreated HIV, ART generally begins within two weeks of TB therapy when CD4 is below 50 and by 8 to 12 weeks when CD4 is at least 50. TB meningitis is an exception in which ART should not begin during the first eight weeks.
Use current pregnancy narratives
Treat active TB during pregnancy promptly. Most LTBI treatment can wait until 2 to 3 months postpartum unless progression risk is high. Do not use 3HP during pregnancy. Use pyridoxine 25 to 50 mg daily with isoniazid.
Preserve breastfeeding context
First-line TB drug concentrations in milk are too low to treat the infant and generally too low to cause toxicity. Breast milk does not replace infant evaluation or treatment.
Redesign for organ dysfunction
Kidney support changes pyrazinamide and ethambutol interval and dialysis timing. Liver disease changes the viability of hepatotoxic regimens. Adjust the complete regimen with TB expertise rather than applying one blanket reduction.
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Lesson
Replace the Legacy Resistant-TB Default
The 2025 guideline supports shorter all-oral regimens for eligible rifampin-resistant disease. The older expectation of 15 to 24 months with routine injectables no longer represents the preferred pathway for many patients.
- Molecular resistance
- BPaLM
- BPaL
- Eligibility
- Toxicity
Use rapid molecular testing and expert consultation.
Susceptibility separates BPaLM from BPaL.
Deliver the complete regimen for the eligible phenotype.
Track QT, neuropathy, blood counts, liver, response, and resistance.
Detect resistance early
Send rapid molecular resistance testing when rifampin resistance is signaled or disease risk is high, while preserving culture and full phenotypic susceptibility.
Use BPaLM for the susceptible-fluoroquinolone pathway
For eligible people age 14 or older with rifampin-resistant, fluoroquinolone-susceptible pulmonary TB, use six months of bedaquiline, pretomanid, linezolid, and moxifloxacin under expert oversight.
Use BPaL for the resistant or intolerant fluoroquinolone pathway
For eligible people age 14 or older with rifampin-resistant pulmonary TB plus fluoroquinolone resistance or intolerance, use six months of bedaquiline, pretomanid, and linezolid.
Respect trial boundaries
Pregnancy, lactation, age under 14, severe extrapulmonary disease, relevant drug resistance or intolerance, and substantial prior bedaquiline or linezolid exposure can require an individualized longer regimen.
Monitor the all-oral toxicity system
Track ECG and QT context for bedaquiline and moxifloxacin, neuropathy and blood counts for linezolid, hepatic injury, interactions, adherence, microbiology, and emergent resistance.
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Lesson
Close the Loop From First Dose to Community Protection
TB cure is both an individual and public-health outcome. Dose delivery, microbiologic conversion, treatment support, contact investigation, toxicity recovery, completion records, and recurrence education must remain connected.
- DOT
- vDOT
- Culture conversion
- Contact investigation
- Completion
Use the least burdensome reliable observation strategy.
Read microbiology alongside symptoms and exposure.
Prioritize confidential evaluation of vulnerable people.
Close doses, response, records, toxicity, and recurrence ownership.
Use patient-centered observation
DOT remains standard for TB disease, and CDC recognizes vDOT as an equivalent alternative when implemented appropriately. Choose the least burdensome reliable approach rather than using observation as punishment.
Investigate a weak response
Persistent symptoms or culture positivity can reflect missed doses, poor absorption, interactions, resistance, inadequate exposure, cavitation, another disease site, or an alternative diagnosis.
Support confidential contact investigation
Give public health accurate exposure dates, settings, disease-site information, smear and culture data, and contact details. Prioritize children and people with HIV or other immune suppression.
Count completion correctly
Verify required doses, interruptions, culture conversion, susceptibility, response, toxicity resolution, final interactions, contacts, and public-health documentation rather than relying only on elapsed months.
End with recurrence ownership
Teach recurrence symptoms, provide the treatment record, identify the follow-up route, and avoid routine imaging or testing that lacks a clinical question after satisfactory response.
Quick check
Module test
Check the connections.
Each attempt draws 10 questions from the complete 180 question bank.
Each attempt draws a fresh set and rearranges the answer choices.
References
Current clinical foundation.
Lecture material was synthesized with the following contemporary guidance. Verify local policy and current guidance before applying clinical information.
- ATS, CDC, ERS, and IDSA 2025 Treatment Update
- CDC Clinical and Laboratory Diagnosis
- CDC Clinical Treatment of Tuberculosis
- CDC Latent TB Infection Regimen Table
- CDC Four-Month Rifapentine and Moxifloxacin Guidance
- CDC Adverse Events During TB Treatment
- CDC Tuberculosis in Pregnancy
- CDC Clinical Care for People with TB and HIV