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Tuberculosis is caused by mycobacterium tuberculosis. In most cases, the disease occurs in the lungs (pulmonary tuberculosis), but tuberculosis can affect all the organs in the body.
Only untreated infectious pulmonary tuberculosis can be transmitted. Tuberculosis that affects organs other than the lungs is usually not contagious.
Tuberculosis is transmitted through droplets containing TB bacteria. When a person with pulmonary tuberculosis coughs, sneezes, speaks, laughs or sings, tiny infectious droplets or aerosols are released into the air. The smallest droplets can pass mucus and cilia and reach the smallest alveoli when inhaled.
Close contacts are most exposed to infection but only a few will become infected.
Contact tracing takes place for every case of pulmonary tuberculosis, see below.
Of those who are infected, only one in ten will go on to develop the disease in their lifetime. This usually happens within the first year after infection, but can also occur after several years. With preventive treatment, this proportion can be reduced dramatically.
People who are only infected, known as ‘latent tuberculosis’, are not sick and cannot infect others.
Pulmonary tuberculosis is the most common form of tuberculosis. The usual symptoms are
- prolonged cough with sputum
- night sweats
- weight loss
Tuberculosis of other organs will cause symptoms in these organs, e.g., tuberculosis in the glands often causes swollen glands.
Detection of infection and disease
To detect infection with tuberculosis, a skin test (Mantoux) and a blood sample (IGRA), or just IGRA are used.
The Mantoux test is introduced as a small blister on the forearm and is read after approximately 72 hours. The swelling (not the redness) is measured in millimetres. If it measures more than 6 mm it is considered positive and over 15 mm is strongly positive.
The Mantoux test can give many false positive results. For example, BCG vaccination can trigger a response. People who are Mantoux positive are tested with an immunological blood test (Interferon-Gamma Release Assay, usually Quantiferon®). The advantage of the IGRA test is that it does not give a positive result from previous BCG vaccination or infection by other mycobacteria. Only taking the IGRA test gives just as reliable results.
The most important tool to determine whether a person is ill with pulmonary tuberculosis is a lung X-ray. The amount og tuberculosis bacteria detected in expectorate from the airways gives an indication of infectivity. The best methods to detect other types of tuberculosis are through clinical examination and detection of tuberculosis bacteria in other organs.
About 350-400 cases per year
Every year in Norway, 350-400 new cases of tuberculosis are registered, i.e., approximately seven cases per 100,000 inhabitants. 318 new cases of tuberculosis were reported in Norway in 2015 (figure 1). All cases of tuberculosis disease must be reported to the Norwegian Institute of Public Health (NIPH).
|Figure 1: Tuberculosis cases in Norway 1990-2015 by place of birth; Norwegian-born (Norskfødte), foreign-born (utenlandsfødte) and total (totalt).|
About two out of three cases are pulmonary tuberculosis. Approximately 85 per cent of new tuberculosis cases occur among immigrants (see figure 1). They are often young adults, half are under 30 years of age and the proportion of men and women is equal. Most are believed to be infected in their country of origin before arriving in Norway.
Norwegian-born patients with tuberculosis are mostly elderly people who were infected when tuberculosis was common in Norway, and who have developed the disease as they become older and weaker. In 2013, there was an outbreak connected to a dance institute in Eastern Norway, where nine people became ill with tuberculosis.
Internationally, drug addicts and homeless people are a risk group for tuberculosis but few cases of infectious tuberculosis are diagnosed so far in these environments in Norway.
Most tuberculosis cases in Norway occur in Oslo, mainly because it is the largest city in Norway and because there is a higher proportion of foreign-born inhabitants than in other regions. Low numbers within each county lead to some random variations from year to year.
DNA studies of bacteria
In Norway, DNA studies are carried out on all tuberculosis bacteria that have been grown in the laboratory. These genetic tests are also called fingerprint studies. These studies give important information when trying to trace a transmission route.
DNA studies show that there is little transmission in Norway between immigrants and from immigrants to people born in Norway. Some exceptions occur; in 2016 there was an outbreak connected to an education institution in Eastern Norway.
After two weeks with correct treatment it is assumed that most pulmonary tuberculosis patients are no longer contagious (patients with other forms of tuberculosis are usually not contagious while untreated). Treatment must usually continue for six months but can take up to two years if the patient is infected with bacteria that are resistant to the most common medications.
To ensure recovery and to prevent development of resistant bacteria it is very important that all treatment is completed. International recommendations require that tuberculosis is treated by having health workers observe patients take their medications every day throughout the treatment period (DOT - Directly Observed Therapy).
Treatment results are good. Although there are exceptions, tuberculosis is a curable disease. Among 324 tuberculosis patients diagnosed in 2014, of these 285 (88 per cent) were treated successfully.
Bacteria that have become resistant to the usual drugs are a serious and growing problem. Multi-resistant bacteria are tuberculosis bacteria that are resistant to both rifampicin and isoniazid, the most important medicines in the treatment of tuberculosis. In recent years, there have been approximately six and eleven multi-resistant tuberculosis cases per year, in 2015 there were six cases. Several more have bacteria that are resistant to just one drug.
Under disease control law, tuberculosis is defined as a dangerous communicable disease. The individual will therefore be recompensed for all expenses for examination, treatment and vaccine. People born outside Norway who are under investigation or treatment for tuberculosis can stay in Norway until treatment is completed.
A number of preventive measures have been introduced to keep tuberculosis under control in Norway:
- BCG vaccine against tuberculosis is offered to groups who, from experience, are more vulnerable to infection than others. This mainly includes infants in families where the mother or father is from a country with high incidence of tuberculosis. The children are offered vaccination when they are 6 weeks old. They are then protected during visits to, or from, their parents' country of origin. Until 2009, all pupils were offered vaccination at secondary school.
Health workers and healthcare students who will have direct contact with patients for more than three months are recommended to take the vaccine. Others who have tuberculosis in their environment are considered particularly at risk of infection and will be offered the BCG vaccine.
- The vaccine does not give full protection against tuberculosis but it does protect against the most dangerous forms of tuberculosis. The vaccine is not proven to be effective in people older than 35 years. It takes about six weeks from vaccination to take effect.
- Asylum seekers and other people from countries with high prevalence of tuberculosis, who plan to stay in Norway for more than three months, are required to undergo tuberculosis testing. Those who may benefit from the vaccine should be offered it.
Countries with high occurrence of tuberculosis
- Also others who have been at risk of infection, or where there is a medical suspicion of infection, are required to be examined. Drug addicts and homeless people in major cities are regularly examined with lung x-rays. The same applies to prison inmates. In the general population, lung X-rays are only used in wider contact tracing.
Preventive treatment: People who are infected with tuberculosis can be offered preventive treatment to reduce the chances of infection leading to disease.
Contact tracing: A person who has been diagnosed with tuberculosis will be part of a transmission chain. Therefore, the Municipal Health Officer must determine whether contact tracing is appropriate. Contact tracing can have two purposes: 1. Find the source of the infection. 2. Find out if the patient has infected others.
Finding the source is relevant if a child or young person is diagnosed with tuberculosis, because then the infection will be recent. Such contact tracing is appropriate for patients with infectious and non-infectious tuberculosis.
Determining if the patient has infected others is only relevant with infectious pulmonary tuberculosis. The people that the patients have had contact with are tested and preventive treatment is provided if needed. The experience from Norway is that it is primarily those who are in close contact with tuberculosis patients over a long time that become infected.
Public plans: All municipalities must have a tuberculosis control programme as part of their Infectious Disease Control Plan. Regional health authorities will have their own tuberculosis control programmes and appointed tuberculosis coordinators.
Notification duty: All cases of tuberculosis must be reported to the NIPH, by regulation from the Ministry of Health and Care Services 2002 (revised in 2009). There are separate rules for the duty of notification.
The tuberculosis bacterium was first detected in 1882. A diagnostic test, (tuberculin tine test) was developed later. The BCG vaccine was available in the 1920s, but was first widely used in the 1940s. Until 1950, tuberculosis was endemic in Norway. The disease has declined with improved living standards, vaccines and new medicines.
The word tuberculosis is derived from the Latin word tuberculum meaning “small knot.”
It is estimated that one third of the world's population is infected with tuberculosis. WHO estimates that in 2015 there were 10.4 million new cases. Most cases occurred in India and China, while Africa has the highest occurrence per 100,000 inhabitants. The problem of co-infection with HIV is also increasing in South-east Asia.
The tuberculosis problem increased throughout the 1990s. This is partly due to incomplete treatment and the development of resistance, plus the HIV epidemic. In particular, there is increased incidence of new cases in Africa and Asia. The number of new cases per 100,000 inhabitants is no longer increasing in Africa and Asia, but due to population increase, the number of patients is still increasing every year in Africa, South-east Asia and the eastern Mediterranean.
Since 1990, there has also been a significant increase in tuberculosis cases in the Baltic countries, Russia, Uzbekistan, Kazakhstan and parts of China. Here, 10-25 per cent of the patients are infected with multi-resistant strains. Since 2001, tuberculosis incidence has declined somewhat in Eastern Europe.
- World Health Organisation (WHO) Europe, the incidence of tuberculosis in different European countries
- European disease control centre in Stockholm
WHO aims to stop the rise of tuberculosis in 2015 and then reduce the number of cases by 2050 so that tuberculosis is no longer a public health problem. This means that the incidence must then be reduced to below one case per million inhabitants. Other organisations that are working to stop the spread of tuberculosis:
- The Union works for the global prevention and control of tuberculosis with emphasis on developing countries
- Stop TB is a worldwide movement that is working to stop the unnecessary spread of tuberculosis
- U.S.A’s Department of Communicable Diseases, Centers for Disease Control and Prevention
Analysis and Registry at the NIPH
The NIPH is responsible for the Norwegian Surveillance System for Communicable Diseases (MSIS) which includes the tuberculosis registry and gives advice about measures to prevent and limit infectious diseases.
Vaccinations and any unwanted effects are registered in the Norwegian Immunisation Registry (SYSVAK). The NIPH distributes the BCG vaccine and tuberculin for testing in Norway.
The national reference laboratory at the NIPH receives strains of all newly diagnosed cases in Norway. Identification, genetic typing, resistance determination and freezing of all of these bacterial strains are carried out.