"[5]Depending on ventilation and other factors, these tiny droplets [from the person who has active tuberculosis] can remain suspended in the air for several hours.
Even after completing the full course of medication, there is no guarantee that the tuberculosis bacteria have all been killed.
[citation needed] "When a person develops active TB (disease), the symptoms (cough, fever, night sweats, weight loss etc.)
Tuberculin (also called purified protein derivative or PPD) is a standardised dead extract of cultured TB, injected into the skin to measure the person's immune response to the bacteria.
So, if a person has been exposed to the bacteria previously, they should express an immune reaction to the injection, usually a mild swelling or redness around the site.
A waterproof ink mark is drawn around the injection site so as to avoid difficulty finding it later if the level of reaction is small.
[19] The area of induration (NOT of erythema) is measured transversely across the forearm (left to right, not up and down) and recorded to the nearest millimetre.
The excess solution is then wiped off and a waterproof ink mark is drawn around the injection site.
Because there has been such a long time since the immune responses to TB has been necessary, that person might give a negative test result.
[22] Boosting is only likely to be relevant if an individual is beginning to undergo periodic TSTs (health care workers, for example).
Therefore, the CDC urges that individuals be treated based on risk stratification regardless of BCG vaccination history, and if an individual receives a negative and then a positive TST they will be assessed for full TB treatment beginning with X-ray to confirm TB is not active and proceeding from there.
[24] Conversely, the UK guidelines acknowledge the potential effect of the BCG vaccination, as it is mandatory and therefore a prevalent concern – though the UK shares the procedure of administering two tests, one week apart, and accepting the second one as the accurate result, they also assume that a second positive is indicative of an old infection (and therefore certainly LTBI) or the BCG itself.
This may lead to treating more people than necessary, with the possible risk of those patients developing adverse drug reactions.
[citation needed] The role of IFN-γ tests is undergoing constant review and various guidelines have been published with the option for revision as new data becomes available.CDC:MMWR Health Protection Agency:UK There are currently two commercially available interferon-γ release assays (IGRAs): QuantiFERON-TB Gold and T-SPOT.TB.
HPA Interim Guidance:The HPA recommends the use of IGRA testing in health care workers, if available, in view of the importance of detecting latently infected staff who may go on to develop active disease and come into contact with immunocompromised patients and the logistical simplicity of IGRA testing.It is usually assumed by most medical practitioners in the early stages of a diagnosis that a case of latent tuberculosis is the normal or regular strain of tuberculosis.
[citation needed] There is no agreement regarding terminology: the terms preventive therapy and chemoprophylaxis have been used for decades, and are preferred in the UK because it involves giving medication to people who have no disease and are currently well: the reason for giving medication is primarily to prevent people from becoming unwell.
[36] A Cochrane systematic review published in 2013 evaluated four different alternatives regimens to INH monotherapy for preventing active TB in HIV-negative people with latent tuberculosis infection.
"Current standard therapy is isoniazid (INH) which reduce the risk of active TB by as much as 90 per cent (in patients with positive LTBI test results and fibrotic pulmonary lesions compatible with tuberculosis[31]) if taken daily for 9 months.
"[12] If a patient were to be cured in the strictest definition of the word, it would mean that every single bacterium in the system is removed or dead, and that person cannot get tuberculosis (unless re-infected).
As such, a person diagnosed with latent TB can safely assume that, even after treatment, they will carry the bacteria – likely for the rest of their lives.
[citation needed] There is controversy over whether people who test positive long after infection have a significant risk of developing the disease (without re-infection).
Some researchers and public health officials have warned that this test-positive population is a "source of future TB cases" even in the US and other wealthy countries, and that this "ticking time bomb" should be a focus of attention and resources.
[38] On the other hand, Marcel Behr, Paul Edelstein, and Lalita Ramakrishnan reviewed studies concerning the concept of latent tuberculosis in order to determine whether tuberculosis-infected persons have life-long infection capable of causing disease at any future time.
Ramakrishnan told the New York Times that researchers "have spent hundreds of millions of dollars chasing after latency, but the whole idea that a quarter of the world is infected with TB is based on a fundamental misunderstanding.
Writing in The Atlantic, science journalist Katherine J. Wu explains:[43]If the bacteria were lingering, researchers would expect to see a big spike in disease late in life among people with positive skin tests, as their immune system naturally weakens.
They would also expect to see a high rate of progression to full-blown TB among people who start taking immunosuppressive drugs or catch HIV.
“If there were a slam-dunk experiment, that’s it,” William Bishai, a TB researcher at Johns Hopkins, told me.The first BMJ article disputing widespread latency was accompanied by an editorial written by Dr. Soumya Swaminathan, Deputy Director-General of the World Health Organization, who endorsed the findings and called for more funding of TB research directed at the most heavily afflicted parts of the world, rather than disproportionate attention to a relatively minor problem that affects just the wealthy countries.
In 2022, the WHO issued corrigenda to its 2021 Global TB Report to clarify estimates on the worldwide burden of infected people.
The corrigenda also removed the prior estimate of the lifetime risk of TB of 5 to 10% among those with evidence of past TB infection, indicating that they no longer have confidence in earlier estimates that a substantial percentage of those with positive immunologic test results will develop the disease.
This article incorporates public domain material from websites or documents of the Centers for Disease Control and Prevention.