Tuberculosis

The earliest known cases of tuberculosis (TB) have been discovered in Egyptian mummies dating back to 4000-2000 BC. TB was probably the leading cause of death in Europe and the US in recorded history. Mortality from TB began decreasing with improved socioeconomic conditions, long before drug therapy and use of the BCG vaccine.

The tubercule bacillus was identified in 1882 and led to early disease control strategies, sanatoriums, pasteurisation of cow’s milk, development of BCG vaccines and discovery of anti-TB drugs.  

Compulsory notification of TB began in New Zealand in 1940. BCG immunisation was first introduced to New Zealand in 1948. Universal screening and vaccination of 13 year olds was discontinued in the South Island in 1963, was phased out in regions of the North Island in the 1980s, and had ceased by 1990. 

Tuberculosis (TB) notification rates in New Zealand have been around 10 per 100,000. Incidence has decreased slightly in recent years to around seven per 100,000.

New Zealand has higher rates of disease in compared to other developed countries. This may be attributed to socioeconomic deprivation and immigration from high-incidence countries. Over two-thirds of all TB cases in New Zealand are in foreign-born individuals.

The highest rates of disease are seen in individuals living in urban areas, particularly Auckland and South Auckland and in people of non-European ethnicity, particularly Pacific People and ‘Other’.

People with tuberculosis may not have any symptoms. When symptoms are present they may include fever, cough, coughing up blood stained phlegm or blood, chest pain, night sweats, weight loss or poor weight gain, anorexia (not feeling like eating) and malaise (tiredness).

The bacteria are coughed out in small droplets and inhaled by another person.

• One person with tuberculosis can infect one quarter to one half of their close contacts.

• Children are more likely to progress from infection to disease than adults. They also have a high risk of developing meningeal TB (infection of the layers over the brain) and miliary TB, both severe forms of disease.
• The tuberculosis strain may become antibiotic resistance, particularly if the full antibiotic course is not taken.
• About half the people with active TB disease will die if they do not receive treatment.

• People in close contact with a known case of TB.
  • Most children are infected from an infectious adult within their own immediate or extended family.
• People residing in institutions, including refugee camps and immigration centres, prisons, rest homes, and mental health facilities.
• People regularly exposure to cattle, deer, possums and certain animal products.
• Occupational contact as a risk factor is poorly documented.
• TB is uncommon in New Zealand people with HIV infection (about 2%).
• Congenital TB (acquired in utero) is rare.
• Breastfeeding does NOT pass TB onto the infant.

Active tuberculosis is treated with a combination of long term antibiotics (six months) that must be taken regularly.

• In New Zealand neonatal BCG vaccine should be offered to infants who:
  • Will be living in a house or family/whānau with a person with either current TB or a past history of TB.
  • Have one or both parents or household members or carers, who within the last five years lived for a period of six months or longer in countries with a TB rate of ≥ 40 per 100,000.
  • During their first five years, will be living for three months or longer in a country with a TB rate of ≥ 40 per 100,000 and are likely to be exposed to those with TB.
• All doctors are legally required notify the Medical Officer of Health of any suspected or proven diagnosis of active TB or reoccurrence of TB.
  • Doctors are not legally required to advise the Medical Officer of Health about people who have a TB infection without active TB but they are requested to obtain permission from the person to do so.
• Public health will identify infected contacts who may require treatment of active TB disease or TB infection, identify uninfected contacts under the age of five years who may benefit from BCG vaccination, identify the source case if not known, identify environmental factors that may be contributing to the transmission of TB and educate contacts about TB.
• Children with active TB are excluded from school until effective antibiotic treatment has started, compliance with treatment is established and any symptoms have decreased.
• Healthcare staff and students should be screened for TB infection before starting work or study.
  • Healthcare staff at high risk of TB exposure should complete an annual questionnaire about TB symptoms and exposure, and have a Mantoux test (tuberculin skin test) or interferon gamma release assay (IGRA) if they previously tested negative.
  • Healthcare staff working in lower-risk areas should complete periodic questionnaires during their employment and be asked to report symptoms consistent with TB.

Tuberculosis in humans is caused by acid-fast bacillus Mycobacterium tuberculosis, Mycobacterium bovis and more rarely Mycobacterium africanum.

One case can infect 25-50% of their close contacts.

Mantoux and IGRA testing

• Mantoux testing (tuberculin skin testing) is recommended for children seven years and under.
• Either a Mantoux test or interferon gamma release assay (IGRA/QuantiFERON®-TB Gold test) can be used for a child over seven years of age.
• IGRA testing is particularly recommended in those who have previously had a BCG, are immune compromised, are a healthcare worker, are unlikely to comply with or unable to manage repeat visits for reading of their Mantoux or sequential testing.
  • IGRA are able to differentiate, reasonably accurately, between a BCG and TB disease immune response to M. bovis in those over seven years of age.

Latent TB

• Diagnosis of latent TB infection (LTBI) is based on evidence of infection in the absence of active or previously active (old) TB disease.
  • The Mantoux test or IGRA is positive in the absence of a past BCG.
  • The person is asymptomatic.
  • Their CXR is normal or only shows trivial and stable evidence of past TB (e.g., a small scar or patch of calcium).
• Generally, if untreated, adults with LTBI have a 5–15% chance of developing active TB disease at some point in their lives.
• LTBI in recently infected adults, children less than five years of age, people living with HIV and people with other immuno-suppressive medical conditions and/or immuno-suppressive treatments has a greater chance of progressing to active TB disease.

Active TB

• In two-thirds of cases TB is contained within the lung (pulmonary TB).
• When TB spreads outside the lungs (extrapulmonary) it can infect lymph nodes, pleura, the skeletal, genitourinary, neurological or cardiovascular systems, abdominal organs, larynx (TB laryngitis), skin, endocrine glands, multiple sites (disseminated TB) or miliary TB.
• Active TB disease may be asymptomatic.
• When symptoms are present they could include cough, fever, night sweats, weight loss or poor weight gain, anorexia and malaise. Later symptoms may include haemoptysis, shortness of breath, chest pain and altered liver function.
• In pulmonary TB a chest x-ray may show lymphadenopathy, pleural effusion, atelectasis, infiltrate, cavitary lesions or miliary disease.
• Diagnosis of TB still relies on chest X-ray and culture of appropriate specimens for acid-fast bacillus (AFB) smear, mycobacterial culture and the histological hallmark of necrotising granulomatous inflammation.
• TB culture still takes time so PCR techniques may provide additional more rapid information.
• Specimens may be obtained via sputum induction, bronchoscopy, fine needle aspiration and biopsy.
• Mantoux testing and IGRA may provide supportive evidence for a diagnosis of active TB.
• Multi-drug resistance (resistant to isoniazid and rifampicin) occurs in less than 1% of all TB isolates in New Zealand.

Tuberculosis is spread through airborne droplets.

• Those younger than 12 years of age are not usually infectious.
• Incubation is usually 2-10 weeks.
• People receiving treatment for TB may continue to be smear-positive for prolonged periods but have significantly reduced infectivity.

• Sociodemographic factors such as poverty, overcrowding and migration from countries of high incidence have been identified as contributing to the disease’s resurgence in New Zealand.
• Tuberculosis (TB) is a communicable disease that is a risk to healthcare workers.
  • The greatest risk to healthcare workers is from a patient who is not suspected of having TB.
• Outbreaks can occur with strains of antibiotic resistant bacilli and in HIV infected people and their healthcare providers.

About 7-10 cases of TB per 100,000 people in New Zealand are diagnosed each year.

The majority of TB cases occur in adults, with the highest rates per 100,000 in those aged 20–29 years followed by those aged 70 and over. The incidence of TB in adults decreased slightly in New Zealand from 2002-2008. Morbidity and mortality from TB also declined slightly over this time.

Almost two-thirds (65%) of TB hospitalisations are in adults, of these adults aged 70 years and over have the highest hospitalisation and mortality rates.

Children less than 15 years of age account for 7–14% of all cases, but this proportion varies significantly by ethnicity (25% of cases in Pacific peoples, 14% in Māori, 5% in Europeans and 4% in ‘Others’). Although the incidence of TB in children has remained low, it has not fallen in recent years.

Asian ethnic groups are 25 times, Pacific peoples 10 times and Māori five times more likely to be infected with TB than Europeans.

Although HIV infection increases a person’s risk of getting TB it is uncommon for HIV positive people in New Zealand to be infected (about 2% from 2004-2008).

Surveillance is important for supporting the local management of TB, monitoring disease incidence and identifying risk factors

• All doctors are required notify the Medical Officer of Health of any suspected or proven diagnosis of active TB or reoccurrence of TB under the Tuberculosis Act 1948.
  • Doctors are not legally required to advise the Medical Officer of Health about people who have a TB infection (latent TB) without active TB but are requested to notify with the permission of the person to do so.
• Public health will identify infected contacts who may require treatment of active TB disease or TB infection, identify uninfected contacts under the age of five years who may benefit from BCG vaccination, identify the source case if not known, identify environmental factors that may be contributing to the transmission of TB and educate contacts about TB.
• Children with active TB are excluded from school until effective antibiotic treatment has started, compliance with treatment is established and any symptoms have decreased.
• Healthcare staff and students should be screened for TB infection before starting work or study, to reduce the risk they have TB and will pass it onto others, particularly vulnerable patients, in the workplace.

The universal use of the BCG vaccination for healthcare staff and students is not advised in New Zealand

• The risk of occupationally acquired TB for most workers is relatively low.
• BCG has low efficacy in adults.
• BCG affects Mantoux test (tuberculin skin test) reactions and causes problems when the Mantoux test is subsequently used as a diagnostic tool.
• This is less of a concern if the healthcare worker screening is performed using interferon gamma release assay (IGRA/ QuantiFERON®-TB Gold test In-tube assay).
• Healthcare staff at high risk of TB exposure should complete an annual questionnaire about TB symptoms and exposure, and have a Mantoux test or IGRA (if they previously tested negative).
  • Conversion of the Mantoux test or IGRA requires a chest x-ray (CXR).
  • If the CXR is normal treatment for latent TB should be considered.
  • If an abnormality is detected the staff member requires further investigation by a respiratory physician.
• Healthcare staff working in lower-risk areas should complete periodic questionnaires during their employment and be asked to report symptoms consistent with TB, particularly if they are working with patients who are immune compromised.
• Routine, periodic CXR screening is not recommended for healthcare workers.
• BCG immunisation will not prevent infection with TB. However, when given just after birth about 70% of infants and young children will be protected from developing severe forms of TB disease i.e. meningeal TB (infection of the membranes covering the brain) and miliary TB.

In New Zealand neonatal BCG should be offered to infants who:

• Will be living in a house or family/whānau with a person with either current TB or a past history of TB.
• Have one or both parents or household members or carers, who within the last five years lived for a period of six months or longer in countries with a TB rate of ≥ 40 per 100,000.
• During their first five years, will be living for three months or longer in a country with a TB rate of ≥ 40 per 100,000 and are likely to be exposed to those with TB.
• Based on the 2009 World Health Organization estimates of TB the following global areas have rates ≥ 40 per 100,000:
  • Most of Africa
  • Much of South America
  • Russia and the former Soviet states
  • The Indian subcontinent
  • China, including Hong Kong
  • Taiwan
  • South East Asia (except Singapore)
  • Some Pacific nations (except the Cook Islands, Fiji, Tonga, Niue, Samoa, Tokelau and Tonga)

The objective of treatment of TB is to achieve a lifetime of cure of the disease while preventing resistance.

• Multi-drug resistant TB (resistance to at least isoniazid and rifampicin) is not a major problem in New Zealand despite a high proportion of imported TB disease.

Latent TB

• Treatment of LTBI in an individual at high risk of developing active TB disease is effective in reducing the individual’s future risk of developing TB disease.
• Treatment regimes take 3-12 months depending on the person’s risk factors, drug regime and compliance with treatment.

Active TB

• Treatment requires multiple antibiotics to which the infecting strain of tuberculosis is susceptible to over a period of time.
• Treatment is usually administered in two phases:
  • The intensive phase of treatment - bactericidal phase (two months in adults, more drugs are used).
  • The continuation phase - sterilisation phase (four months in adults, fewer drugs are used).
• Poor adherence to prescribed anti-TB treatment is the most common cause of treatment failure.
• Directly observed therapy (DOT), where a health professional supervises the person taking their anti-tuberculosis medication after discharge home is an effective way to monitor adherence to treatment.
• All patients with TB who smoke should be advised and offered support to quit smoking.
• With the exception of central nervous system TB, miliary/disseminated TB and bone and joint TB, extra-pulmonary TB is treated with the same drug regimens as pulmonary TB.
• Corticosteroids may be added for some forms of extra-pulmonary TB when adequate anti-tuberculosis treatment is being given.
• People with positive sputum cultures should have repeat cultures at least monthly to confirm sterilisation from TB.
• Baseline serology, full blood count, creatinine, ALT, hepatitis B surface antigen, hepatitis C and HIV, should be completed in all adults who are to be treated for TB disease or latent TB infection. Depending on the patients risk factors for hepatotoxicity, monitoring of either ALT or liver function tests should occur in all patients on treatment for TB.
• Patients should be advised of common and important side effects, e.g. those associated with hepatitis and ocular toxicity, and to report these promptly.
• Healthcare staff must support patients and enable them to adhere to the full course of treatment.