Tuberculosis

Epidemiology of TB
Definition
• Tuberculosis (TB): A chronic infectious disease mainly caused by a bacterial
microorganism called Mycobacterium tuberculosis or tubercle bacillus.

Epidemiology
• Tuberculosis is endemic in most developing countries including Sub Saharan Africa.
• Tuberculosis has become one of the most serious threats to public and individual health in Africa.
• In 1993 World Health Organisation (WHO) declared Tuberculosis a global emergency.
• The disease is responsible for millions of lives lost each year.
• Africa bears the highest burden of the disease with an incidence rate (in 1997) estimated
at 260 per 100,000.
• During the same year, Africa had a population of 610 million whom 211 million (approximately 35% of the population) were thought to be infected with tuberculosis.
• Tuberculosis is on the increase, especially in countries with a high prevalence of HIV
• If patient left untreated or inadequately treated, tuberculosis can kill or render the patient disabled for life.
• Due to its frequency and severity, tuberculosis remains an important disease of public health significance.

Transmission
• The most important source of infection is an individual with TB of the lungs.
• The transmission of these tubercle bacilli occurs by airborne spread of infectious droplets.
• The infectious individual spreads the bacilli during:
o Coughing
o Sneezing
o Singing,
o Spitting
o Talking
o Exhalation
• Good ventilation removes nuclei droplets and so prevents nuclei to be inhaled by a
susceptible person.
• Direct sunlight kills tubercle bacilli within minutes, but they can survive in the dark for many hours (24-48 hours).

• Transmission therefore generally occurs indoors
• Factors that determine an individual’s risk of exposure include:
o The concentration of droplet nuclei in contaminated air
o The length of time he/she breathes that air
• TB of cattle (bovine TB) occurs in some countries through milk and may infect the tonsils presenting as scrofula (cervical lymphadenitis), or the intestinal tract causing abdominal TB.
The main species for this sort of TB is called Mycobacterium bovis.
• The risk of progression from infection to disease depends on the status of the immune system.

• The majority (90%) of people without HIV infection who are infected with
Mycobacterium tuberculosis do not develop tuberculosis disease because their immune system is strong enough to prevent the development of disease.
o TB infection is just presence of Mycobacterium tuberculosis in the body but the patients has no symptoms or signs of TB
o TB disease is refers to presence of the Mycobacterium tuberculosis in the body with asigns and symptoms of TB
• The development of an intercurrent disease or condition that suppresses an individual’s
immune system triggers the dormant bacilli to become metabolically active and causes
the infection to progress to tuberculosis disease.
• Infection with HIV is currently the most common cause of immunosuppression in Tanzania and most of the sub-Saharan Africa.
• People with TB infection and HIV have a >50 times higher risk of developing
tuberculosis disease during their lives than people without HIV infection.
• The risk of developing active TB disease in an HIV negative person is 5-10% per
lifetime. The risk of developing active TB disease in an HIV positive person is 5-10% per year.
• Malnutrition, recurrent infections of any kind, diabetes mellitus can also cause
reactivation of the TB infection into TB disease.

Clinical Features
• The most common symptoms of pulmonary tuberculosis are:
o Persistent cough for 2 weeks or more; every patient presenting with this symptom should be regarded as a suspect
o Sputum production, sometimes bloodstained (haemoptysis)
o Shortness of breath
o Chest pain
o Fatigue (tiredness)
o General malaise
o Loss of appetite
o Loss of weight
o Night sweats
o Fever
• The symptoms for extra-pulmonary tuberculosis depend on the organs involved, for example:
o Chest pain from pleurisy
o Swelling of lymph nodes in tuberculosis lymphadenitis
o Pain and swelling of joints in tuberculosis arthritis
o Deformity of the spine with or without neurological deficit in TB of the spine (Pott’s disease)
Headache, fever, stiffness of the neck and mental confusion in tuberculous meningitis (TBM)

Diagnosis of Different Forms of TB
• There are two main types of tuberculosis based on the clinical manifestations.
• These are:
o Pulmonary tuberculosis (PTB)
       This is the commonest that affects the lungs and is the infectious form of the disease.
o Extra-pulmonary tuberculosis (EPTB)
       This is the form that affects organs other than the lungs e.g. pleura, lymph nodes, pericardium, spine, joints, abdomen or genito-urinary tract.
       It may actually affect any part of the body.
• The diagnostic approaches are different in the two types as described below.

Pulmonary Tuberculosis in Adults
• The diagnosis can be done using sputum smear for AFB, chest X-Ray and culture as outline below:
o Sputum smear for AFB
       The diagnosis of tuberculosis rests mainly on the identification of the tubercle bacilli by sputum smear microscopy.
     Mycobacteria are ‘acid-fast bacilli’ (AFB) seen as red rods when properly stained using Ziehl Nielsen (ZN) staining technique and visualized under bright field microscopy.
     Every tuberculosis suspect should submit at least two sputum specimens for smear microscopy within 24 hours following the schedule below:
The patient is given a sputum container for collection of the second specimen.
Morning Patient produces the next early morning specimen and returns it to the
diagnostic centre.
o Chest X-ray
      Diagnosis of tuberculosis using chest X-ray is not reliable because there are other chest diseases that may produce similar changes for instance, HIV infection further diminishes the reliability of chest x-ray in the diagnosis of tuberculosis, therefore, should be diagnosed whenever possible by sputum examination.
         Chest x-ray findings suggestive of pulmonary tuberculosis in patients with a
smear negative microscopy should always be supported by clinical findings and a
medical officer experienced in TB should decide on the diagnosis.
       However, the utility of x-ray to hasten the diagnosis of smear negative pulmonary among HIV positive should be encouraged wherever available.
     Note that, there is no chest X-ray appearance typical for PTB.
      Most times a chest X-ray is not necessary when the sputum result is positive.
o Sputum culture
      Culture is a more sensitive method to detect mycobacteria than AFB microscopy and can detect as low as 10 bacilli/ml of sputum.
     However, culture methods are slow, expensive and available in few well equipped hospitals.
• Other investigations that can be done
o Tuberculin skin test (TST):
     Tuberculin is a purified protein derived (PPD) from attenuated mycobacterium.
     A person who has been infected with tuberculosis develops hypersensitivity to
tuberculin, which is measured in millimetres in duration of 48-72 hours after the tuberculin injection has been given in the skin.
    A positive TST is >10mm induration in patients without HIV and > 5mm
induration in patients with HIV.
    A positive TST however only means a patient may be infected with TB but does
not imply active TB disease.
     Immunosuppressive conditions such as HIV infection, malnutrition, severe
bacterial infections such as TB itself, viral infections e.g. measles, cancers, and
incorrect injection of PPD may give false negative tuberculin results.
     The tuberculin skin test is valuable as a diagnostic tool in young children.
ƒ In a child who did not receive a BCG, an induration of 10mm or more is
interpreted as positive.
o Erythrocyte Sedimentation Rate (ESR)
       The measure of the ESR is non-specific and should not be used as a routine for tuberculosis.
       In most patients with bacterial infection (including TB) the ESR is raised but a normal ESR does not exclude TB disease.
Extra-Pulmonary Tuberculosis
• Extra-pulmonary TB is a tuberculous disease occurring in organs other than the lungs.
• Extra-pulmonary TB is common in HIV-positive patients.
• If a patient has extra-pulmonary TB as well as pulmonary TB should be classified as a pulmonary tuberculosis case.
• It is therefore important to examine sputum specimens from patients with extra-pulmonary TB.
• There are several types of Extra-pulmonary tuberculosis as described below.
o TB-lymphadenitis
        Usually TB lymphadenitis presents as a group of firm to fluctuant, may be tender
and might break through the skin.
     This can result in a chronic sinus or ulcer that heals with scarring.
    Diagnosis is by taking biopsy of the lymph node or aspiration of the fluid/pus if the lymph node is fluctuant.
o Pleural effusion, pericardial effusion, and tuberculous ascitis
     Inflammatory tuberculous effusion may occur in the pleural, pericardial or
peritoneal cavities.
     These conditions are more frequently seen in HIV positive individuals.
      It is difficult to isolate the organisms from this kind of fluids.
     Supportive features in the diagnosis include the appearance of the fluid, high
protein in the fluid and increased white blood cells (lymphocytes) in the fluid.
o Spinal TB
      Tuberculosis of the spine (Pott’s disease) is a severe form of extrapulmonary tuberculosis.
       The TB infection starts from the inter-vertebral disc and spreads along the anterior side to the adjacent vertebral bodies.       
        The collapse of the vertebral bodies might compress the spine causing
neurological deficit (paralysis).
      The diagnosis is made with a plain X-ray of the affected vertebral column.
o Miliary TB
       Miliary TB is blood-borne dissemination of tuberculosis from either a primary infection or erosion of a secondary tuberculous lesion into a blood vessel (TB bacteremia).
       Miliary TB is common in late stage of HIV and AIDS disease.
       The patient presents with signs and symptoms of septicemia with fever, wasting, confusion etc.
       The diagnosis is sometimes made with the help of a chest X-ray that shows
uniformly distributed miliary (like millet seeds) shadows.
o TB meningitis
        TB of the meninges may occur from a rupture of a cerebral tuberculoma into the subarachnoid space or blood born dissemination from active infection from
elsewhere in the body.
       Most times, patients present with headaches, decreased consciousness and neck stiffness.
      The diagnosis usually rests on clinical grounds and microscopic examination of
cerebrospinal fluid and biochemical tests.

Diagnosis of Tuberculosis in Children
• The diagnosis of TB in children can be very difficult owing to the wide range of
symptoms.
• Sputum cannot often be obtained from children and in any case it is often negative even on culture.
• Symptoms in children are not typical.
• The diagnosis should therefore be based on:
o Clinical findings (especially failure to thrive or weight loss)
o Family history of contact with a smear positive case
o X-ray examination
o tuberculin testing
o Culture (if available)
o Non-response to broad spectrum antibiotic treatment
• A score chart below can help to reach the diagnosis of tuberculosis.
• Older children who are able to cough up sputum should go through the same assessment
as adults using smear microscopy.

Posted by
Welfare Jambo