Guidance

Background to TB contact tracing guidance

Published 6 October 2026

Background

TB is a notifiable infection under The Health Protection (Notification) Regulations 2010 No. 65 (11, 12). UKHSA publishes reports annually on TB notifications in England. In 2024, England remained just under the World Health Organization (WHO) threshold to maintain its TB low-burden status of less than 10 cases per 100,000 population (incidence 9.4 per 100,000 per annum), data is presented at the current rate of increase, England will pass this threshold by end of 2026 (13).

Contact tracing of individuals who have been exposed to a person diagnosed with TB disease is a strategy used to interrupt onward transmission by identifying, finding, assessing and offering diagnostic testing and treatment to those people who have had contact with them while they were considered infectious.

Contact tracing forms a cornerstone of TB prevention in England, data is reported annually in the TB Prevention Chapter of the annual report (14, 15). In 2024, a total of 9,676 contacts were identified from 2,980 people notified with pulmonary TB who had contact information recorded. Further analysis showed that this identified 182 people with active TB disease and 1,276 people with TB infection (LTBI). This equates to 75 people with active TB and 523 with LTBI being identified for every 1,000 index individuals contact traced, highlighting the high value of contact tracing investigations as an active case finding tool (13) as well as for the identification of TB Infection (LTBI).

The aims of contact tracing are to:

• identify people with TB disease (active TB) who may a source of the infection or secondary case who can be offered treatment for TB disease, TB Preventative Treatment (TPT) to reduce their lifetime risk of developing TB

• identify and treat secondary cases of TB disease early – people who have been exposed to an infectious TB case may already have TB disease (finding them early allows prompt treatment, reducing illness and onward transmission)

• prevent further transmission – by identifying infectious contacts and initiating treatment, contact tracing helps stop ongoing transmission within households, workplaces, schools and other settings

• identify vulnerable contacts at highest risk – young children, people with HIV and those who are immunocompromised are more likely to progress rapidly to TB disease and need prompt assessment and protection

• assess the extent and settings of transmission – contact tracing helps public health teams understand where and how transmission occurred, informing decisions about whether investigations need to be expanded

• support TB elimination goals – most future TB cases arise from untreated latent infection, systematic contact tracing is a core strategy for long‑term TB control and elimination

• raise awareness in individuals of their potential exposure to infectious TB and the promoting earlier presentation, identification and treatment

• identify contacts under 16 years of age in whom TB infection is not detected and for whom Bacillus Calmette-Guerin (BCG) vaccination may be appropriate as per Immunisation against infectious disease, Tuberculosis – the Green Book, chapter 32 (16)

Clinical features of TB infection (LTBI) and TB disease (Active TB)

The natural history of M. tuberculosis infection in a host is complex. TB was traditionally categorised as occurring in one of 2 states: either as Latent TB infection (LTBI), or active TB disease. In this binary model, LTBI was considered as a state where there has been infection with viable but metabolically inactive M. tuberculosis and the individual has no symptoms, disease or infectiousness on account of a controlling immunological response (detectable by an Interferon-Gamma Release Assay (IGRA) or tuberculin skin test (TST). By contrast, active TB disease was present where the M. tuberculosis has become metabolically active, and the individual has become symptomatic or there are detectable TB bacteria microbiologically or there are radiological signs of disease (for example on chest X-ray or CT scan).

There is now an evolving recognition that TB in humans exists beyond the binary states of latent infection or active disease. New classification systems are being developed to better represent the continuous and dynamic spectrum on which TB infection and disease occurs, inclusive of the more recently recognised categories of incipient and subclinical TB (17). Therefore, this document will make recommendations for contact tracing based on the newer classifications TB disease (active TB) and TB Infection (TBI) previously categorised as latent TB infection (LTBI). For clarity, TB infection will be referred to as TB infection (LTBI) throughout this document.

The highest risk of TB infection being transmitted to others occurs within the household of a person with active TB disease (18). It has been estimated that 5 to 10% of all immunocompetent people who are infected with M. tuberculosis will progress to clinical TB disease in their lifetime, with approximately half of the overall lifetime risk in the first 2 years after infection. Therefore, there is a preventative value of prompt contact tracing where the objective is to identify those most recently infected who are therefore at high risk of progression to active TB disease (19, 20).

The remaining 90 to 95% of immunocompetent people who were exposed to a case of infectious TB will either eliminate the infection or continue to control it and not progress to a disease state (21, 22). The risk of TB infection progressing to TB disease is much higher in patients living with, or who acquire, compromised immune systems, see section on Vulnerability of contacts and Appendix 2.

Symptoms of TB disease

TB disease can affect the lungs (pulmonary) or can affect any part of the body, with the most common extrapulmonary sites in individuals in England being the lymph nodes, pleura, bone and central nervous system (CNS) (13). The symptoms of TB disease are varied and depend on the sites affected. General (systemic) symptoms may include fever, loss of appetite, weight loss, night sweats and fatigue and, in children, failure to gain weight and height.

More than half of people with TB notified in England in 2024 had pulmonary disease (54.3%, 2,983 out of 5,490) (13). Pulmonary TB typically causes a persistent (at least 3 weeks) productive cough, which may be accompanied by blood-streaked sputum or haemoptysis (coughing up blood). If left untreated, TB may be a slowly progressive disease in most otherwise healthy adults, which may eventually be fatal.

All patients with pulmonary and laryngeal (affecting the larynx) TB are considered potentially infectious and contact tracing should be initiated. In addition there may be transmission in limited situations from non-pulmonary disease (23). Following a diagnosis of TB disease, the clinical team caring for the individual will need to assess the infectiousness of that person.

When undertaking contact tracing an ongoing risk assessment is required on each occasion when new evidence of transmission is demonstrated in a setting. Individuals who are screened for TB as part of contact tracing may be found to have TB disease (active TB) or TB Infection (LTBI).

When TB Infection (LTBI) is identified, it is often not possible to determine when a person was infected – transmission may have occurred from the index case, or the individual may have had pre-existing TB infection (LTBI) prior to contact with the index case. Transmission from an index case is supported if the contact had a baseline negative IGRA result taken at the time of exposure, which converts to a positive result on subsequent testing after 6 to 8 weeks (24).

People with TB Infection (LTBI) have no symptoms of TB disease and feel well. As the TB bacteria is metabolically inactive the person with TB Infection cannot pass TB onto others and is not considered to be infectious. TB infection (LTBI) can re-activate and result in the symptoms of TB disease as described above.

Treatment of TB infection (LTBI) with TB chemoprophylaxis or TB Preventative Therapy (TPT) is effective at reducing the future risk of TB disease (25). Current diagnostic tests for infection have a low predictive value in identifying those who are at highest risk of disease progression to TB disease. Current estimates are that between 25 and 100 people who test IGRA positive may need to be treated with TB chemoprophylaxis to prevent a single occurrence of TB disease (26, 27).

Terminology

The following terminology is used in this guidance document. These definitions should be used in discussions and decision-making in relation to a TB case. This list does not include all definitions and during incident and outbreak (IMT) investigations, specific case definitions should be agreed by the IMT or outbreak control team (OCT) and will dependent on the specifics of the incident or outbreak following the principles of management.

Background information about active TB investigations can be found in Appendix 1.

Case definitions

The definitions below are derived from those of WHO and other sources (2, 28, 29). Case definitions are based on the certainty of the diagnosis and on whether laboratory confirmation is available. Cases are also classified according to anatomical site of disease, bacteriological results, radiographic findings, age, and immunological status. TB infection (LTBI) may also be diagnosed in individuals, which may indicate M. tuberculosis transmission, but does not constitute a case of TB.

Case of TB disease

An individual has TB disease, when there is the presence of symptoms or signs of TB, in addition there may be laboratory confirmation for example microbiologically detectable M. tuberculosis, radiological changes or histological changes indicative of TB disease.

A case of TB is a person diagnosed with active disease caused by Mycobacterium tuberculosis, based on clinical, radiological, and/or laboratory evidence. WHO defines TB disease as current, active illness rather than latent infection.

TB cases are further classified by site of disease (pulmonary vs extrapulmonary) and bacteriological status (confirmed vs not confirmed).

Index person

The index person is the first identified case of new or recurrent TB disease in a person of any age in a setting in which others may have been exposed; a contact tracing investigation will be centred around this person. Although the index case may be the first detected person with TB disease in a place or setting; the source of their infection may be found to be one of their contacts (the primary case); however, the person who presents first is regarded as the ‘index case’.

Every newly identified person with pulmonary or laryngeal TB should be considered as an index case for contact tracing purposes.

Confirmed person or ‘case’ of TB disease

A confirmed person or case of TB disease is an individual with a clinical specimen which is either:

• culture positive for a M. tuberculosis complex organism [note 1]
• PCR positive for M. tuberculosis complex (if patient has not been treated for TB in the past – PCR positivity can last more than 2 years after the completion of appropriate treatment) (30, 31).

Note 1. (Culture positive cases in England will be confirmed and undergo WGS through the National Mycobacterial Reference Service (NMRS) or through the Wales Centre for Mycobacteria depending on the location of the laboratory isolating the organism).

Clinical case

A clinical case (may also be termed ‘probable’, ‘presumed’ or ‘presumptive’ case) is an individual without a laboratory microbiological confirmation, but:

• a clinician has confirmed that the individual’s clinical and/or radiological signs or symptoms are compatible with TB disease
• a clinician has decided to treat the patient with a full course of anti-TB therapy

Clinical cases may also be supported by detection of caseating granulomata on histological examination, in the absence of positive M. tuberculosis culture or PCR results.

Children are often clinical cases due to the paucibacillary, (that is, a low bacterial load, despite the presence of disease) nature of their disease and challenges of obtaining specimens to confirm diagnosis by culture (32).

Possible case

A possible case is an individual who presents with symptoms and signs of TB and is awaiting clinical or diagnostic evaluation and is not on TB treatment.

Infectious TB

For the purposes of this guideline, any case of pulmonary or upper respiratory tract (including laryngeal) TB disease is considered potentially infectious. This includes cases who are smear-negative on spontaneous sputum but smear-positive on induced sputum or BAL.

It also includes cases who are smear-negative but culture-positive on any respiratory samples (including sputum, induced sputum and BAL) or never culture-confirmed pulmonary disease.

For considerations of infectiousness of such cases, see the section on infectiousness of cases.

This definition diverges from the previous 2023 RCN guidance, which does not refer to BAL samples, upper respiratory tract TB or cases in which respiratory samples are smear-negative3. The RCN guidance is currently being re-drafted.

TB infection (latent TB infection)

An individual may be diagnosed with TB infection (LTBI) when all the following criteria are met:

• the individual has evidence of a response to M. tuberculosis antigens, for example in the person testing positive on at least one of the following tests (demonstrating a host response):

  • Interferon Gamma Release Assay (IGRA)
  • TB antigen-based skin test (TBST)
  • purified protein derivative (PPD) positive tuberculin skin test (TST)/Mantoux test
• the individual has not previously been treated for TB
• an absence of symptoms and signs of TB disease
• no radiological evidence of TB disease (for example on chest X-ray of CT scan)

People with TB infection (LTBI) do not have symptoms and cannot transmit infection to others. TB infection (LTBI) may later progress into TB disease. TB infection refers to a state of immune response to stimulation by Mycobacterium tuberculosis antigens, indicated by a positive tuberculin skin test (TST) or interferon-gamma release assay (IGRA) test, with no evidence of active TB disease.

Contact tracing definitions

Contact tracing is a recognised public health activity used to identify and break chains of transmission to help reduce the spread of infectious diseases. For TB the purpose is to identify people who have been exposed who may already have TB disease or have TB infection (LTBI). Early treatment can be offered to people who have already acquired TB disease reducing further transmission TB preventative treatment (TPT) can be offered to those with TB infection reducing the overall risk of progression to active disease.

It is a systematic investigation process intended to identify previously undiagnosed TB disease or TB infection (LTBI) among the contacts of an index case.

Contact investigation consists of 2 components:

• identification and prioritisation of people who have been in contact with a person with infectious TB during the infectious period
• clinical evaluation of the person that has been in contact to assess if they have TB disease or TB infection (LTBI) requiring treatment ^{[footnote 1]}

This section focuses on the terminology used in the identification and prioritisation of contacts as well as those used to determine the infectious period and describe a setting where TB exposure may have taken place.

Contacts

A contact is anyone who has been directly exposed to a person with infectious TB.

Contacts are defined as:

• individuals who have spent time with someone with infectious TB
• or individuals who have spent time with a child (under 16 years) diagnosed with TB (affecting any part of their body) and may be the initial source of the child’s infection

Contacts can be sub-categorised by duration of exposure, their susceptibility to infection (age, immune status), type of contact and type of environment within which the exposure occurred.

Close contacts

Close contacts are individuals who have had prolonged or frequent close exposure to an individual with confirmed or clinical, infectious TB during the infectious period (see below)

Close contacts may include:

• people living and/or sleeping in the same household and share a bedroom, kitchen, bathroom or communal area
• pupils who share dormitories
• intimate partners or sexual partners
• frequent visitors to the household such as members of the wider family or friends who may stay for periods
• people living in a house of multiple occupation (HMO), hostel or asylum seeker accommodation where there are shared facilities
• people who attend other congregate settings (see below for examples)
• healthcare workers (HCWs) if adequate infection prevention and control (IPC) precautions have not been observed, including personalised protective equipment (PPE), particularly during aerosol generating procedures (AGPs), as defined in the national infection prevention and control manual (NIPCM) for England (34)

This list is not exhaustive and should be considered in context for any individuals when there is prolonged contact with an infectious case of TB.

Casual contacts

Generally, all contacts other than close contacts, such as social contacts or work colleagues are classified as casual contacts. Some casual contacts may be assessed as being close contacts following risk assessment depending on the duration of time spent with the index case.

Congregate setting

A congregate setting is an environment where several people meet or gather and share the same space for an extended period of time on a regular basis. When used in the context of TB contact tracing a congregate setting is a place where people live, work, or spend extended periods together in close proximity, often sharing enclosed air space.

Examples may include:

• workplaces
• schools
• childcare and educational settings
• healthcare settings
• social care settings and social venues
• HMOs
• places of detention
• places of worship

Infectious period

For the purposes of contact tracing, it is recommended that the estimated start to the infectious period for a pulmonary or laryngeal case of TB is 3 months before the onset of respiratory symptoms or 3 months before the first finding consistent with TB disease, whichever is earlier (8).

This recommendation is more cautious than the previous 2023 RCN guidance, which recommends using the start of symptoms or (if asymptomatic) 3 months prior to the start of treatment (3). HPTs may, through their risk assessment, determine a more appropriate start point for contact tracing (considering settings, findings on household contact screening, symptom history and clinical advice for example).

Completion of 2 weeks of effective treatment is conventionally regarded as the time point at which individuals with fully sensitive TB disease will be rendered non-infectious (35, 36). However, this has been challenged in several more recent studies and the actual time taken to become non-infectious is affected by factors including the extent of cavitary disease (in which lung tissue has been destroyed), drug susceptibility and adherence to prescribed TB treatment (37, 38).

The infectious period should be assessed on an individual basis using information including clinical response, known susceptibility of the TB to treatment being used, adherence to treatment and sputum smear conversion or improvement.

The US National Tuberculosis Controllers Association and Centre for Disease Control advised in 2005 that the infectious period is closed when the following criteria are satisfied:

• effective treatment (as demonstrated by M. tuberculosis susceptibility results) for at least 2 weeks
• diminished symptoms
• mycobacteriological response (for example decrease in grade of sputum smear positivity detected on sputum-smear microscopy) (39).

The definition of non-infectiousness for multi-drug or rifampicin-resistant (MDR/RR) TB is more conservative, not because MDR/RR-TB is more infectious, but because the consequences of transmission are more severe. WHO recommends a minimum of 2 consecutive sputum samples that are culture negative at 8 weeks, taken at least 1 week apart, before the index individual is considered non-infectious and able to de-isolate (40, 41, 42).

Duration of exposure (to infectious TB)

The duration of exposure indicates the amount of time a person was in contact (exposed) to the person with infectious TB. It is not possible to determine a minimum time under which transmission will not occur, and there is little evidence to support any specific time limits in terms of infection risk (43). The risk depends on how infectious the case is, how close and repeated the contact is, environmental factors such as ventilation alongside the potential vulnerability of the person exposed.

In most instances, TB transmission occurs from contact over more prolonged periods, hours and days. However, more limited casual exposure may lead to transmission, particularly if the case is sufficiently infectious, environmental conditions are favourable and/or if the contact is vulnerable.

As standard, a first round of contact tracing for infectious TB should be all household and regular social contacts (irrespective of estimated contact duration). In addition all contacts who meet a locally agreed threshold of duration of contact during the index cases infectious period. It is current ‘custom and practice’ to use a minimum of 8 or more hours total of cumulative contact time between an index case while they are infectious and immunocompetent contacts to provide a framework for prioritisation when implementing screening exercises (3).

For vulnerable contacts (see Appendix 2), 4 hours or more total cumulative contact time may be adopted. These time periods are arbitrary. They should be used as a guide, rather than a definitive metric, acknowledging the different risk profiles that exist and will be further informed by the local dynamic risk assessment and investigations.

Dynamic risk assessment

A dynamic risk assessment (in the context of TB contact tracing) is the process of an ongoing evaluation of how infectious the index case was to their contacts and how likely the infection was to be passed onto other people exposed. The risk assessment in relation to how wide to contact trace should be informed and reviewed as more information becomes available, such as the individual’s microbiological results, or the number of contacts identified as either TB disease (active TB) or TB Infection (LTBI) in initial rounds of contact tracing. The Incident or Outbreak management team may review the duration of contact time and/or extended tracing in cases where dynamic risk assessments have indicated this may be necessary on account of high suspected infectiousness and transmission.

TB incident

Where significant TB exposure has occurred in a setting outside the household, for example at a school, workplace, hostel or detention centre, it is called a TB incident.

TB outbreak

A TB outbreak is when there are more TB cases than expected within a geographic area or population during a particular time period, and there is evidence of recent transmission of M. tuberculosis among those cases (44). The term TB situation or TB incident can be used alongside the term outbreak.

TB cluster

The UKHSA National Mycobacterial Reference laboratories (NMRS) performs Whole Genome Sequencing (WGS) for all culture confirmed cases of TB that are received. These are then subjected to TB clustering analysis. A TB cluster is identified where a group of TB strains cultured from different individuals have closely related genomes. Refer to the guidance in the UKHSA WGS Handbook.

Clustering may help define the extent of an outbreak or may help identify additional epidemiological links to standard contact investigations or ‘missed’ contacts (45).

Transmission of TB

Almost all cases of TB in the UK are acquired through the respiratory route, from a person with infectious respiratory, pulmonary and/or laryngeal TB. In the majority, the identified pathogen is M. tuberculosis (97.7% of culture-confirmed cases in 2024), with a small number of infections from other members of the MTBC (13). Other members of the MTBC tuberculosis include:

• M. bovis
• M. africanum
• M. microti
• M. caprae
• M. pinnipedii
• M. canetti
• M. orygis
• M. mungi

There will likely be additional elements required for the public health response for zoonotic species, such as involvement of the Animal and Plant Health Agency (APHA) which are outside of the scope of this document.

M. tuberculosis is transmitted through the air. When people with pulmonary or laryngeal TB disease breathe, cough, sneeze, shout, or sing in indoor settings, infectious particles can be expelled and, depending on the environment, can remain suspended in the air for several hours (46, 47).

Transmission occurs when a person inhales infectious particles containing M. tuberculosis, which travel through the respiratory system to reach the alveoli of the lungs. The likelihood of TB transmission depends on several factors, which include the infectiousness of the index case, the environment in which contact occurs, the duration of contact between the case and their contacts, and the vulnerability of the contacts. It is important to consider all these factors together when conducting a risk assessment and deciding upon the contact tracing approach. These factors are expanded upon below and summarised in Table 1.

Infectiousness of index case

Site of TB disease (anatomical site)

The anatomical site of TB disease refers to the part of the body that the TB disease is affecting. TB can affect the larynx (laryngeal), lungs (pulmonary) or can be or exclusively extrapulmonary. Extrapulmonary TB disease occurs in places other than the lungs, including the lymph nodes, the pleura, the brain, the kidneys, or the bones and joints; TB disease can occur anywhere in the body. People with extrapulmonary TB disease are usually not infectious, however contact tracing investigations can be undertaken to identify a ‘source’ for that person’s TB disease.

The site of the TB disease affects its infectiousness; laryngeal TB cases (while rare) are 4 to 5 times more infectious than smear positive pulmonary cases (9, 48, 49). Cases of exclusively extrapulmonary TB are typically non-infectious, and contact investigations are instead aimed at preventing further transmission by identifying the source of the TB for the index case. This is especially important where the is evidence of recent infection, such as TB in a child. Extrapulmonary TB may also become transiently infectious under some circumstances, for example, in a healthcare setting, where there is aerolisation of drainage fluid from an abscess with a high concentration of organisms (50).

Nature and duration of symptoms

The nature of a person’s symptoms, for example when they have had a cough and the length of time of their symptoms may affect their infectiousness. Individuals with a cough that is productive (brining up mucus or phlegm referred to as sputum) or frequent are considered more infectious than those without (8). However, it is increasingly appreciated that asymptomatic, subclinical TB is a significant contributor to TB transmission globally (51). The longer a person with tuberculosis disease remains symptomatic and untreated, the greater the opportunity for exposure to others and the higher the likelihood of transmission to additional individuals.

Microbiological factors

Microbiological factors such as smear status, TB polymerase chain reaction (PCR) status and time to laboratory detection by culture all contribute to the assessment of the infectiousness of a person with TB disease. The terms smear status refers to microscopic examination of a sputum sample for the presence of acid-fast bacilli (AFB). A positive smear indicates that the TB bacteria are detected in the person’s sputum.

Individuals with smear-positive pulmonary disease are, in general, considered more infectious than those with smear-negative disease (10, 33). Observational studies showed that household contacts of smear-positive patients were 2 to 12 times more likely to be infected with M. tuberculosis than household contacts of smear-negative patients (52).

Although posing a lower risk than smear-positive people, smear-negative pulmonary cases can still transmit TB to others and are estimated to contribute towards 13 to 20% of TB transmission (33, 53).

Molecular test results may provide supportive information when assessing potential infectiousness in tuberculosis such as the level of positivity in a PCR test. The Xpert® MTB/RIF Ultra assay reports results in semi quantitative categories (high, medium, low, or trace).These categories have been found to strongly correlate with smear grade and time to culture positivity, and reflect mycobacterial burden. Therefore they may be informative about the infectiousness of the person with TB (54).

Some individuals with medium or high-grade TB- Xpert® MTB/RIF Ultra TB PCR (Cepheid) positivity are smear negative but have a short time to positive culture, indicating a high bacterial burden. Where routine access to Xpert® MTB/RIF Ultra TB PCR (Cepheid) is available, some TB services are using this as an independent parameter contributing towards contact tracing decision-making to assess infectiousness. Other TB PCR tests are commercially available.

Radiological features

The appearance of TB on a chest x ray or CT scan shows the radiological nature of pulmonary disease and indicates the extent of disease or presence of cavities which also contributes to assessment of infectiousness (56).

Environment

The environment shared by a person with active TB plays an important role in the transmission of the disease. People who spend time in close proximity to someone with active TB have a higher risk of becoming infected. The risk is greatest when individuals share a small, poorly ventilated space with the person who has TB, compared with sharing a larger, well‑ventilated space.

Transmission from a person with infectious TB tends to occur more frequently in close contacts who live in the same household with enclosed air-sharing space, than in their social and work contacts (57, 58). The size of the room in which contact occurred and the number of air changes per hour (ACH, defined as the number of times that the total air volume in an environment is completely removed and replaced in an hour) are important environmental factors to consider in TB transmission. TB infection control guidelines for healthcare recommend 6 to 12 air-changes/hour room ventilation to reduce transmission in high-risk settings (59, 60).

Duration of contact

The longer the time that an index case with infections TB is in contact with other people, the more likely it is that they will transmit TB to them. Contacts living in the same household or sleeping in the same room as the index case are most at risk, and this may be due to the length of time they are exposed to the case. However, transmission is known to occur outside of the household. TB transmission after brief interaction, especially in vulnerable contacts, has been described (61).

A person with infectious TB may transmit infection to several people before they have been diagnosed and received sufficient effective treatment to render them non-infectious. Studies suggest that one sputum smear-positive patient with pulmonary TB will infect, on average, 10 to 15 others for every year they remain symptomatic and untreated (62).

In 2024, the median time between symptom onset and diagnosis for people with pulmonary TB in England was 73 days. Approximately one-third of people experience a delay of more than 4 months between symptom onset and treatment initiation (13). Such delays provide significant windows of opportunity for transmission to others.

Vulnerability of contacts

TB is more likely to both be transmitted to and progress to active disease in contacts living with, or who acquire, compromised immune systems. These groups should be prioritised for contact tracing. The risk of TB infection (LTBI) progressing to active disease in a person living with uncontrolled human immunodeficiency virus (HIV) is approximately 5 to 15% per annum (63). This is higher than for people with competent immune systems where the lifetime risk is between 5 and 10%. The WHO highlights that people living with HIV are at up to 20 times higher risk of developing active TB compared to those without HIV infection.

Additional risk groups include older age (≥65 years), low weight, immunosuppression related to co-morbidities (such as diabetes mellitus and chronic renal failure) and immunosuppression related to pharmacological agents (some biological therapies, anti-rejection drugs for organ transplantation, chemotherapy and systemic steroids). NICE Link (1.2) regarding testing in >65 years.

When contact tracing, the age of the person who is a contact should also be taken into account during the risk assessment process. BAPT consider children as those aged under 16 years including adolescents, and highlight that they are more susceptible to progression to TB disease following infection with M. tuberculosis (19). A retrospective cohort study of nearly 45,000 contacts of active TB in Florida followed over 15 years found children aged 0 to 15 years showed an over 9 times risk of subsequently being diagnosed with culture-confirmed M. tuberculosis disease compared to adults aged 25 to 44 years (64). The risk of progression to disease was highest in children under 5 years of age, and particularly those under 2 years of age (65).

Table 1: Summary of factors to consider to assess TB transmission

Factor	Detail
Infectiousness of index case	Anatomical site of disease – laryngeal, pulmonary are considered infectious TB. Review if case is considered to be exclusively extrapulmonary. Nature and duration of symptoms - productive or frequent cough. Microbiological factors – smear status, TB PCR status, time to detection by culture. Radiological nature of pulmonary disease - extent of disease, presence of cavities.
Environment	Size and ventilation of environment Number of air changes per hour (ACH)
Duration of contact	Duration of contact with the index case while they were infectious – how frequent was the contact and over what time period
Vulnerability of the contacts	Extremes of age (young children and older adults) People with immunocompromise due to co-morbidities or pharmacological agents.

Testing for TB infection (LTBI) is not routinely offered for contacts over 65 years of age. In asymptomatic close contacts older than 65 years, chest X-ray may be considered (if there are no contraindications), possibly leading to further investigation for active TB. More information on diagnosing latent TB in adults is available in the NICE clinical guidance section 1.2.

References

See the attached list of references for TB contact tracing guidance.

1. Note: Testing for TB infection (LTBI) is not routinely offered for contacts over 65 years of age. ↩