19-07-2025
Cy-TB test introduced by Kerala govt. for detecting and treating tuberculosis
The State health authorities in Kerala have introduced a new intradermal test called Cy-TB for detecting and treating tuberculosis (TB) infection following the prioritisation of latent TB infection treatment under the National TB Elimination Programme (NTEP).
TB infection is different from active TB disease. A person with TB infection harbours the organism causing TB infection (Mycobacterium tuberculosis) in the body, having probably acquired it through contact with someone with active disease. But the organism remains dormant or inactive in the body and the person neither has any TB symptoms nor is he contagious.
However, if left untreated, 5-10% of them will progress to developing active TB disease when the body's immune system weakens, allowing the TB bacteria to flare up. This could happen within weeks of acquiring the infection or maybe years, depending on the immune system and other factors determining immune regulation.
Study
A community-based cross-sectional study among adults in Thiruvananthapuram district in 2023 had reported that roughly one-fifth of the adult population in the district – 20.5% of adults – have tuberculosis infection. The study, 'Prevalence of Tuberculosis Infection among Adults of Thiruvananthapuram District of Kerala as Measured by Interferon Gamma Release Assay – A Cross-Sectional Study,' tested whole blood samples of 396 adults in Thiruvananthapuram for TB infection and found that the prevalence of TB infection increased with age, ranging from 11.5% in the 18-35 age group to 30.3% in the 58-years-plus age group.
'Our studies show that about 22% of the State's general population has acquired TB infection from the community. While they pose no immediate threat to the community, once they go into an immuno-compromised state, the bacteria will multiply and produce symptoms of active disease. Given the morbidity profile of Kerala – high prevalence of diabetes, chronic kidney disease, heavy alcohol use and a huge population on dialysis – it is important that we identify and treat these people to reduce the future burden of TB,' says Aparna Mohan, Government of India-WHO consultant for TB.
Cy-TB is a third generation test approved by the Central TB Division.
Blood test detection
Since 2021, Kerala has been using the blood test Interferon Gamma Release Assay (IGRA) for detecting TB infection. However, this test required extensive laboratory support and it had a waiting period too. There were also systemic difficulties in rolling it out.
Cy-TB is a highly specific, accurate and user-friendly skin test, wherein 0.1 ml dose of M. tuberculosis-specific antigens (ESAT-6 and CFP-10) are injected into the skin in the inner forearm. An induration (a raised area) of 5 mm or more which develops on the skin within 48-72 hours indicates TB infection (While a trained nurse can administer the injection, the person will have to return to the health centre for checking out the skin reaction.)
If tested positive, active TB has to be ruled out before considering TB preventive therapy. TB preventive therapy is optional and not currently recommended for all those who are infected. Only high risk individuals recommended for preventive therapy under the NTEP alone need to take preventive therapy.
Risk groups
In Kerala, the identified risk groups include individuals on immunosuppressive therapy, those with silicosis (lung disease following the inhalation of silica dust), those on anti-TNF treatment, and those on dialysis and awaiting organ transplantation. Preventive therapy is also offered to health-care workers who test positive in the Cy-TB test.
The preventive therapy is a short regimen with less number of drugs. This could be three-month weekly Isoniazid and Rifapentine (3HP) or six-months daily Isoniazid (6H).
According to the State TB Division, Cy-TB will be offered in district TB centres, taluk hospitals, at the block level in some districts and in all dialysis centres too. The Health department also intends to use Cy-TB to test inmates in old age homes where pulmonary TB has been reported. The test is currently available in major private hospitals too.
