Tuberculosis Flashcards
What is tuberculosis (TB)?
Tuberculosis infection is caused by a bacterium called tubercule bacilli.
How is TB transmitted?
TB is spread by droplet from cough by people with pulmonary TB. The bacillus is inhaled into the lung.
What are the different types of mycobacteria that can cause TB?
Mycobacterium tuberculosis complex includes Mycobacterium tuberculosis (MTB) and non-tuberculous (atypical) mycobacteria.
Who is at risk of TB?
Those at risk for TB include people who are deprived (homeless, malnourished, overcrowded, vitamin D deficient), those with alcohol abuse, those in prisons, those who are immunocompromised (diabetes mellitus, HIV, steroid use), the elderly, and those who have contact with high-risk groups (certain jobs, travel to areas of high incidence).
What are the clinical presentations of pulmonary TB?
The clinical presentations of pulmonary TB include cough (productive and not improving with standard antibiotics), haemoptysis, chest pain, fever, night sweats, fatigue, and weight loss.
How is TB diagnosed?
TB can be diagnosed using a tuberculin skin test, chest x-ray, sputum culture, and nucleic acid amplification tests.
What is the treatment for TB?
The treatment for TB includes a combination of antibiotics, such as isoniazid, rifampicin, pyrazinamide, and ethambutol, for at least 6 months.
what is the route of infection for TB
what is the progression of tb
What are the initial hypersensitivity reactions seen in TB infection?
Erythema nodosum and Phlyctenular conjunctivitis.
What is the majority of cases caused by pulmonary MTB?
the majority of cases (55%) of TB are caused by pulmonary MTB.
What is cavitatory disease in pulmonary TB?
Cavitatory disease is a more infectious form of pulmonary TB.
What is a Ghon focus in the lungs?
Ghon focus is an area of central caseation and fibrosis in the lungs caused by MTB.
What is the microbiological diagnosis of MTB?
The microbiological diagnosis of MTB includes sputum/BAL, ZN stain, TB cultures 6-8 weeks, nucleic acid amplification, and PCR.
How is MTB diagnosed using Mantoux test and IGRA/T-spot test?
MTB can be diagnosed using Mantoux (Tuberculin test) and Interferon gamma release assay (IGRA)/T-spot test. The host responds to MTB infection by a delayed Type 1V hypersensitivity reaction to the tubercle bacilli, and diagnostic tools that are based on this cellular immunity have been developed.
What are some characteristics of MTB bacillus?
MTB is an aerobic bacillus that divides every 16-20 hours (slow). It has a cell wall, but lacks a phospholipid outer membrane. It does not stain strongly with Gram stain (weakly positive) but retains stains after treatment with acids, making it an acid-fast bacillus.
What are some diagnostic tools used to identify MTB complex and distinguish it from non-tuberculous infection?
Nucleic acid amplification is used to identify MTB complex and distinguish it from non-tuberculous infection, by detecting mycobacterial DNA in various body fluids such as pleural fluid, cerebrospinal fluid (CSF), urine, etc.
What are the stains for MTB
Ziehl-Neelsen stain: bright red bacilli on blue background
Auramine-rhodamine stain using fluorescence microscopy
What kind of inflammation is associated with MTB infection?
Granulomatous inflammation
What kind of cells are typically seen in the center of granulomas in MTB infection?
Infected macrophages (giant cells)
What is the significance of cytokine secretion in MTB infection?
Secretion of cytokines (IFNγ) activates macrophages to kill bacteria
Are acid-fast bacilli typically present in granulomas in MTB infection?
Yes, acid-fast bacilli are often present in granulomas
What is the purpose of the mantoux/ tuberculin test?
To measure the cutaneous immune response to an intradermal injection of purified protein derivative (PPD)
Is the tuberculin test specific for MTB?
No, it can be cross-reactive with other Mycobacterial antigens, making it non-specific
Can the tuberculin test be falsely negative in certain individuals?
Yes, it may be falsely negative in severely ill or immunosuppressed individuals
What kind of immune response is required for a positive tuberculin test?
A delayed hypersensitivity reaction mounted by circulating memory T-lymphocytes
What is the IGRA/T_spot test used for?
To measure T-cell activation by MTB antigens in vitro
How does the IGRA/T_spot test differ from the tuberculin test?
The IGRA/T_spot test is more specific and correlates better with degree of exposure than the tuberculin test
Can the IGRA/T_spot test differentiate between latent infection and active disease?
No, it cannot differentiate between latent infection and disease
What is required for accurate interpretation of the IGRA/T_spot test?
The results must be interpreted carefully together with all other available information
What factors are typically considered in the diagnosis of TB?
History of contact with smear positive TB, signs and symptoms suggestive of TB, abnormal CXR, positive tuberculin or T-spot test, culture of mycobacterium TB
Should HIV testing be considered in the diagnosis of TB?
Yes, HIV testing should always be considered
What is the difference between primary TB and latent infection?
Primary TB is active disease that occurs soon after initial infection, while latent infection is the majority of cases where the immune system has memory of exposure to TB and the risk of reactivation increases with immunosuppression
What is the risk of reactivation in latent TB infection?
2-23% of cases are at risk of reactivation disease, which increases with immunosuppression
What is the difference between latent and active pulmonary TB?
Latent TB is the state where most people infected with TB are asymptomatic and not infectious, whereas active TB occurs when the infection progresses to symptomatic and infectious TB.
What is the chance of progressing to active TB after a person becomes infected with TB?
The chances of progressing to active TB are greatest within 1 to 2 years of infection and decrease steadily after this.
What are the differential diagnoses of TB?
The differential diagnoses of TB include bilateral hilar lymphadenopathy, sarcoidosis, and lymphoma.
What are the sites of extrapulmonary MTB?
The sites of extrapulmonary MTB include lymph nodes, CNS, bone (Pott’s disease of the spine), genitourinary system, GI tract, and disseminated TB (miliary TB).
What is TB lymphadenitis?
TB lymphadenitis is the enlargement of lymph nodes due to TB infection, which can worsen on treatment and form sinus tracts with chronic discharge or cold abscess formation.
What are some differential diagnoses for TB?
Bilateral hilar lymphadenopathy, Sarcoidosis, Lymphoma, Clinical symptoms (B symptoms)
What are some sites of extrapulmonary TB?
Lymph nodes, CNS, Bone (Pott’s disease of the spine), Genitourinary system, GI tract
What is paradoxical reaction and what condition can it be seen in?
Paradoxical reaction is when symptoms worsen on treatment. It can be seen in TB lymphadenitis.
What is miliary TB and what are some common symptoms?
Disseminated miliary TB is a condition where the TB bacteria spread throughout the body. Symptoms include fevers, sweats, weight loss, malaise, respiratory symptoms, GI or CNS symptoms
What are some sites of extrapulmonary TB?
Pericardium, eye, skeleton, genitourinary, gastrointestinal, CNS (Tuberculous meningitis, TB in CSF)
What are the first line drugs used for TB treatment in the initial phase and the continuous phase?
Initial phase: Isoniazid, Rifampicin, Pyrazinamide, and Ethambutol. Continuous phase: Isoniazid and Rifampicin.
what are the side effects of pyrazinamide
may cause hepatoxicity, joint pain, and nausea/vomiting;
what are the side effects of rifampicin
Rifampicin may cause hepatoxicity, reddish color to urine and tears;
what are the side effects of ethambutol
Ethambutol may cause peripheral neuropathy, optic neuropathy, and gout
what are the side effects of isoniazid
Isoniazid may cause hepatoxicity, fever, peripheral neuropathy, and optic neuritis;
What are the side effects of the first line drugs used for TB treatment?
All of these drugs may cause nausea and skin rashes.
What is Multi-drug resistant TB (MDRTB)?
MDRTB is a form of TB that is resistant to treatment with first line drugs due to lack of compliance. Patients with MDRTB must be isolated as they pose a huge public health risk.
What is the treatment for Multi-drug resistant TB (MDRTB)?
A prolonged course of second line drugs, for up to 24 months, may be required. Third line drugs may also be required. MDRTB is managed in centers with expertise and experience.
What is the treatment for Latent TB?
3 months of Rifampicin and Isoniazid or 6 months of Isoniazid.
What is BCG vaccination?
BCG vaccination is offered to infants aged 0-4 weeks to reduce the risk of TB meningitis and miliary TB. It is offered to those born in high incidence areas, with a family history of TB in the last 5 years, or with a parent or grandparent born in a high incidence area.
What is contact tracing for TB?
Contact tracing is identifying the index case (the patient with TB) and then identifying and screening close contacts (e.g. household members, school, work) for the disease.
What is directly observed therapy?
Directly observed therapy is a strategy to ensure compliance with TB treatment, particularly for patients who need supervision due to a chaotic lifestyle, alcoholism, previous TB history, or mental health problems. Parents can supervise children swallowing tablets. Compliance is monitored via hospital visits, video, or local pharmacy.
What are the recommended monitoring tests for TB treatment?
Blood tests, including liver function tests, should be taken at baseline. The Ishihara test, a color vision test, should also be performed. Liver function tests should be monitored.
