Medical and biological significance of exhaled M. tuberculosis detected by community level face mask sampling in Pretoria.

Globally, tuberculosis (TB) is the greatest cause of disease and death by a single bacterial agent. Over one quarter of humanity is estimated to be infected with Mycobacterium tuberculosis (Mtb), the agent of TB; however, more than 80% of those infected never develop the disease because the infection remains quiescent and does not produce symptoms. In order to survive, Mtb must spread from person to person in droplets exhaled by infected individuals. The standard view has been that this only occurs in people who have symptoms of lung TB such as coughing, weight loss and fever. Detecting, diagnosing and treating these individuals as early as possible after they become infectious has been the major priority of the global campaign to eradicate TB. Nonetheless, authorities such as the World Health Organisation (WHO) recognise that many millions of newly infectious cases are missed every year; these undoubtedly fuel the continuing epidemic.
Researchers are now questioning whether people with quiescent TB may also transmit the infection. Evidence for such 'incipient' forms of TB comes from sophisticated lung imaging and direct detection of Mtb in some individuals without symptoms.
Our research team has been working for several years on the use of adapted face masks to detect exhaled Mtb. Masks containing a Leicester-developed synthetic sampling matrix are worn for 30 minutes then the matrix is taken out and analysed for captured Mtb by detecting its DNA in the WHO-recommended Gene Xpert system. Combined with evidence that the face mask sampling (FMS) approach can detect early lung TB, the simplicity, convenience and low cost of FMS led us to investigate whether it could be used to detect infection in a community sampling programme. In a currently active MRC project, the Leicester-Pretoria team have found an unexpectedly high Mtb detection rate: while prior estimates led us to expect a positive rate of up to 1%, in practice this has exceeded 15%.
Our study is based in the Tshwane district where the Pretoria team have developed a community oriented primary care (COPC) programme directed to patient and household centred health promotion. Community Health Workers (CHWs) have been trained in FMS and gather relevant related demographic and clinical data. A youtube video (Breathcatcher) explains the approach to both CHWs and clients.. We have responded by refocussing the current study on caring for those with positive samples. Although we have clear evidence that people with FMS-detected Mtb can progress to conventionally recognised disease within 1-2 months, this has not been detected so far in the current study where our capacity for follow up is very limited. (Ongoing clinical support is provided by the COPC)
In the new study we aim to provide detailed follow up on 50 participants providing Mtb positive masks (CASES) for a full year and to compare their clinical and laboratory status with a comparator group whose mask result is negative (CONTROLS). Tests additional to FMS (including blood and lung imaging) will allow us to compare our evaluations against current diagnostic standards. Review will be monthly for cases and 3 monthly for controls. This approach will allow us to detect different patterns with which individuals exhale Mtb over time and whether their infections progress to active disease. Our work will be supervised by an international monitoring group who will scrutinise our results and advise on the best management of individuals with evidence of disease. In this way they will receive the earliest treatment justified by accepted standards.
This work will provide a description of exhaled Mtb in the Tshwane community and its relation to clinical disease. If, as we suspect, many people without symptoms are contributing to transmission of the infection, a major refocussing of control and treatment will be necessary.

Through face mask sampling (FMS), we are identifying exhaled M. tuberculosis (Mtb) in a pilot active case finding (ACF) study to detect individuals with pulmonary TB (pTB). Working with the community oriented primary care programme in the Tshwane district of Pretoria (RSA) we have found exceptionally high positivity rates (>15% against a prior estimate of <1%) through unselected household sampling. These findings raise concerns that FMS+ve individuals have active TB and are infectious. Although we have evidence from a pilot ACF study that some FMS+ve individuals progress to overt TB in 1-2 months, no clinically recognised pTB has yet been detected in the Tshwane study. Current follow up is very limited and we now seek to place this important finding into context with recent concerns that much TB transmission may come from asymptomatic infection.
Through further sampling on the established Tshwane platform, we will recruit individuals, FMS+ve for Mtb at first contact (cases), into one year follow up allowing us to establish the main patterns of bacillary excretion (e.g. persistent, intermittent and transient) and their clinical status through monthly review. Control individuals, negative on two masks at recruitment, will be matched to cases by HIV status, age and sex, to cases and followed 3 monthly, also for one year. (Target, 75 in each group; expected retention 50)
In addition to Xpert assays on masks, we will detect live Mtb in both masks and blood with a novel bacteriophage assay (recently reported positive in blood from symptomless contacts of pTB). We hypothesise that that blood positivity may predict disease progression.
In addition to providing participant care supervised by an independent study monitoring group, we aim to assess potential for a future study of FMS+ve asymptomatic individuals for their infectivity to guinea pigs in the Pretoria AIR facility, thereby definitively establishing their likely contribution to TB transmission.

Through the further development of FMS we aim to deliver a new approach to the assessment of TB and its transmission in both clinical and community settings. The simplicity and low cost of the approach have enabled its application in marginal communities in South Africa.

Favourable evaluation here will deliver:
1. A means of detecting Mtb exhalers in the community irrespective of their symptoms.
2. An assessment of the relative value of FMS against symptom and sputum-based screening.
3. A means to place single FMS positive results in the context of current diagnostic standards for pTB and the potential roles of novel assays (phage assay on mask and blood) to assist in this.
4. A potential early means of detecting pulmonary TB in communities that does not require individuals to produce sputum or attend a clinic. Early treatment, if justified, is clearly linked to reducing transmission

Comments below all assume that further FMS application continues to reveal exhaled Mtb at high rates. Development towards the impacts described is outlined in the Pathways to Impact document.
We emphasise that TB control is just one of the applications of FMS. The approach can and is being developed to assess all airborne microbes in a format compatible with routine clinical practice.

WHO WILL BENEFIT AND HOW?
ORGANISATION LEVEL PUBLIC HEALTH AUTHORITIES; THE WORLD HEALTH ORGANISATION; DEPARTMENT OF HEALTH; HEALTH PROTECTION ENGLAND; GOVERNMENTS; THE HEALTHCARE INDUSTRY.
Identification of FMS positive individuals within a community will enable refocussing of control efforts on these individuals and their contacts. This approach could rapidly impact on transmission and prevalence of disease. Evidence supporting this approach would lead to significant changes in TB control strategies funded and implemented by the organisations listed. In addition to production of the sampling system and the downstream analysis of samples, the approach creates new opportunities for the healthcare industry to develop products directed to limiting transmission

MEDICAL COMMUNITY AND PATIENTS AND THOSE AT RISK OF EXPOSURE TO MTB.
FMS will enable practitioners to recognise and manage likely infective patients and to obtain microbiological confirmation of diagnosis in those who do not produce sputum. A simple test recognising infectivity based on samples that can be obtained from everyone who can wear a mask will be of great value to practitioners, hospital managers, patients and their contacts. Currently, in the UK patients considered infectious, particularly those with drug resistant infections are maintained in isolation at considerable cost until they are sputum culture negative; if they don't produce sputum then they are evaluated by bronchoalveolar lavage. While much work will needs to be done to establish the negative predictive value of FMS for transmission risk, the potential is clear.

PHARMACEUTICAL INDUSTRIES AND CHARITIES E.G. - GLOBAL ALLIANCE FOR TB DRUG DEVELOPMENT.
While there are no obvious opportunities for new drug development here, the capacity to recognise infectivity will allow evaluation of different treatments in this regard. In the case of resistant infections, existing drugs may differentially affect infectivity. Moreover, our parallel studies on the biological basis of Mtb aerosol transmission (MR/PO23061/1) have potential to identify and transmission-specific bacterial targets.