Dr hadeel fadshil FIBMS
Tuberculosis
a bacterial disease that is important as a major cause of disability & death in many
parts of the world.
The initial infection usually goes unnoticed; tuberculin skin test sensitivity appears within 2-10 weeks. Early lung lesions commonly heal, & leave no residual change except pulmonary or tracheobronchial lymph node calcification.
**About 90-95% of those initially infected enter this latent phase from which there is life long
risk of reactivation.
** 50% of persons with advanced HIV infection, the initial infection may progress directly to pulmonary TB or by lymphohematogenous bacilli to pulmonary, miliary, and meningeal or other extrapulmonary involvement.
Serious outcome of the initial infection is more frequent in infant, adolescent, young adults & immunosuppressed.
Progressive pulmonary TB arises from exogenous re-infection or endogenous reactivation of a latent focus remaining from the initial infection, if untreated about half of patients will die within 5 years, a majority of these within 18 months.
Extrapulmpnary TB occurs less commonly than pulmonary TB. Children & persons with immunodeficinces such as HIV infection have a higher proportion of extrapulmonary TB.
Mortality & morbidity rates increase with age, male, poor, & usually higher in cities than in rural areas.
HIV is the most powerful factor known to increase the risk of progression from TB infection to disease.
TB is considered as social stigma & it has a negative impact on financial resources of the patients.
Although TB disease ranks low among communicable diseases in infectiousness per unit time of exposure, the long exposure of some contacts, household may lead to a 30 % risk of becoming infected.
Epidemics have been reported among people lived in enclosed spaces, such as nursing homes, shelters for homeless , hospitals, schools, prisons & office building.
From 1989 to early 1990, extensive outbreaks of multidrug resistance TB have been recognized in settings where many HIV infected persons are lived.
These outbreaks have been associated with high mortality rates.
Reservoir:
Primarily human, rarely cattle & other mammals are infected.
Infectious agent
* Mycobacterium tuberculosis complex
This complex includes :
---M.tuberculosis and M. africanum primary from humans
--- M.bovis primary from cattle
Mode of transmission:
1- exposure to tubercle bacilli in airborne droplet produced by people with pulmonary or laryngeal TB during expiratory efforts such as coughing, singing or sneezing.
2- Health care workers are exposed during medical procedures such as bronchoscopy, autopsy & intubations.
3- Direct invasion through mucus membrane or breaks in the skin may occur but is extremely rare.
4- Bovine TB results from exposur to tuberculous cattle , usually by ingestion of unpasteurized milk or dairy products & some times by airborne spread to farmers & animal handlers.
Incubation period:
From infection to primary lesion or significant tuberculin reaction about 2-10 week. While the subsequent risk of progressive pulmonary or extrapulmonary TB is greatest within the first year or two after infection.
Latent infection may persist for a life time.
HIV infection appears to increase the risk greatly & shorten the interval for the development of TB disease.
Period of communicability:
As long as viable tubercle bacilli are being discharged in the sputum.
The degree of communicability depends on:
1- Number of bacilli discharged.
2- The virulence of the bacilli.
3- Adequacy of ventilation.
4- Exposure of the bacilli to sun or UV light.
5- Opportunities for their aerosolization by coughing, sneezing , talking or singing or during a high risk medical procedures like autopsies, intubations or bronchoscopes.
Effective antimicrobial chemotherapy usually eliminates communicability within a few weeks, at least in the household setting.
Susceptibility & resistance:
The risk of infection is directly related to degree of exposure & not to genetic or other host factors.
The most hazardous period for development of clinical disease is the first 6-12 months after infection.
The high risk groups are:
1- Children under 3 years old, lowest in later childhood & high again among adolescent, young adult.
2- Very old people.
3- immunosuppressed as HIV, for adults with latent TB infection who are also infected with HIV, the lifetime risk of developing disease arises from 10% to 60-80%.
4- Those underwt or under nourished.
5- Chronic diseases such as CRF, CA, silicosis, DM, postgastrectomy, or substances abuses.
Diagnosis:
A- Case finding methods:
The following methods offer the best prospect for significance yields of cases:
1- Examination of patients with relevant symptoms who present themselves on their own initiative at health facilities (passive case finding).
The most important symptoms are: cough more than 3 weeks, sputum production & wt loss.
Most patients with pul TB may have respiratory symptoms: hemoptysis, chest pain, SOB or fever, night sweat, tiredness, loss of appetite.
2- the promotion of awareness on the community, the medical profession & all medical staff concerning the respiratory symptoms notably persistent & productive cough(more than 3 weeks) & is complicated with blood stained sputum, chest pain, & loss of wt, fever or night sweat.
3- The examination of household contacts of all smears positive TB patients.
4- The bacteriological examinations of patients who for any reasons had radiological examinations of the chest showing an abnormality with appearance of TB.
B- the bacteriological examinations of the sputum is made by demonstration of acid fast bacilli in stained smears from sputum or other body fluids. The diagnosis is confirmed by isolation of organisms on culture.
C- X-ray diagnosis of pul TB is unreliable because other chest disease can look likes TB on X-ray & pul. TB. May show many forms of radiological abnormality.
D- Tuberculin test: immunocompenent people who are infected with M tub. Will usually react to tuberculin skin test. A positive reaction is defined as either 5, 10, or 15 mm indurations based on the risk of exposure or disease.
10-20% of persons with active TB disease may not have any reaction to this test. Therefore, a negative skin test dose not rules out active TB disease.
@ Indications for annual screening tuberculin skin testing in asymptomatic individuals include:
1- HIV infection.
2- Close contact with cases of active TB (includes health care workers, prison guards, and Mycobacteriology laboratory personnel).
3- The presence of a medical condition that increases the risk of active TB (e.g., silicosis, diabetes mellitus, long-term therapy with glucocorticoids or other immunosuppressive medications, hematological or reticuloendothelial malignancies, end-stage renal disease, hemodialysis patients, alcoholism, gastrectomy, jejunoileal bypass, organ transplant recipients, or conditions associated with rapid weight loss or chronic malnutrition).
4- Low-income population (e.g., homeless, injection drug users).
5- Residence in a long term care facility (e.g. correctional institutions, mental institutions, and nursing homes).
@If the above risk factors are absent, a single TST is appropriate in the following patients:
1- A single potential exposure to TB (e.g., diagnosis of TB in a family member) without risk factors for repeated exposures in the future. If the patient is being tested shortly after exposure, (i.e., before delayed hypersensitivity might have developed), then a skin test should be repeated in approximately six to 12 weeks.
2- Presence of an incidentally discovered fibrotic lung lesion.
3- Immigrants and refugees from countries with a high prevalence of TB (e.g., most countries in Latin America, Asia, and Africa).