One in five exposed to TB during HIV clinic visits, Malawi study finds

As many as one in five people attending an HIV clinic in Malawi had prolonged exposure to another patient with potentially infectious tuberculosis (TB) during the course of a year, according to a review of how people subsequently diagnosed with active TB overlapped in clinic attendance with other patients, published in the journal AIDS.

The findings highlight the need for better infection control measures in HIV clinics nearly a decade after deficiencies in infection control in these settings first began to be highlighted by researchers in southern Africa and by the World Health Organization (see NAM’s publication HIV & AIDS Treatment in Practice on this issue, from 2008).

TB is a bacterial infection spread by airborne droplets that can persist in the air for several hours after being coughed up. Poor ventilation and lack of light increase the time that infectious particles linger but mycobacterium tuberculosis is swiftly dispersed by fresh air and killed by sunlight or ultraviolet light. Overcrowded, poorly ventilated spaces greatly aid the transmission of TB.


infection control

Infection prevention and control (IPC) aims to prevent or stop the spread of infections in healthcare settings. Standard precautions include hand hygiene, using personal protective equipment, safe handling and disposal of sharp objects (relevant for HIV and other blood-borne viruses), safe handling and disposal of waste, and spillage management.


A specimen of tissue or other material taken from part of the body and smeared onto a microscope slide for examination. A Pap smear is a specimen of material scraped from the cervix (neck of the uterus) examined for precancerous changes.

sputum smear

A diagnostic test in which a sample of spit is examined under the microscope for the presence of micro-organisms.



A medical treatment using radiation (also known as radiation therapy). Beams of radiation may be produced by a machine and directed at a diseased area from a distance. Alternatively, radioactive material, in the form of needles, wires or pellets may be implanted in the body. Many forms of cancer can be destroyed by radiotherapy.

active TB

Active disease caused by Mycobacterium tuberculosis, as evidenced by a confirmatory culture, or, in the absence of culture, suggestive clinical symptoms.

The risk of TB transmission in healthcare settings can be reduced by:

  • Adequate ventilation and airflow away from congregate settings (spaces where a number of people share the same space for a period of time)
  • Outdoor waiting areas wherever the climate permits
  • Reducing waiting times and crowding by minimising visits to the facility for medication collection or follow-up by 'stable' patients with fully suppressed viral load
  • Separation of TB waiting areas and clinic rooms from other areas
  • Separation of patients with known or suspected TB, and use of cough monitors (recording devices which measure frequency of cough) to triage patients for symptom screening
  • Educating all patients about cough hygiene (covering the mouth and nose when coughing or sneezing, no spitting).
  • Using UV radiation filters where budget permits
  • Developing and communicating a facility-wide infection control plan.

TB is highly prevalent among people with HIV in southern Africa. Up to 18% of people starting antiretroviral therapy (ART) in southern Africa are diagnosed with TB, indicating the high volume of people attending ART clinics who may have undiagnosed TB.

Researchers in Malawi wanted to understand the potential impact of this high burden of undiagnosed TB on the risk of transmission in healthcare settings. They looked at all patients who attended one large HIV clinic in the Karonga district in northern Malawi over one year in 2014 and 2015.

The Karonga clinic provides HIV testing and counselling, antiretroviral treatment and TB diagnosis and treatment. In theory, these services are provided in different spaces within the clinic, but in practice patients mingle, entering through the same door and moving through the corridors of the clinic.

To examine the potential exposure risk, they screened all patients starting antiretroviral treatment for TB, and also screened people after three and six months on ART. Screening was carried out using both a symptom screen and a sputum smear test. Negative smear tests were followed up with an Xpert MTB/RIF test to identify any smear-negative, TB-positive patients.

For every TB case diagnosed, researchers identified the number of patients who attended the clinic on the same day. They assumed that the person with TB had been infectious for six weeks before the date of diagnosis and would continue to be infectious for two weeks after starting treatment.

A total of 5011 people attended the clinic during the study period and made 19,426 visits to the clinic. Sixty-three per cent were women, 76% were HIV positive, 12% attended as caregivers and 5% were current TB patients.

One hundred and sixteen people were diagnosed with TB, of whom 90 attended the clinic at least once before diagnosis or during the two-week period before treatment could be expected to stop transmission.

The median time spent in the clinic was 81 minutes. Overall, 10,812 clinic visits (58% of all visits) took place when no patient was judged likely to have been exposed to infectious TB, but the remaining 42% of visits had some potential exposure and 3473 (18.9%) had at least one hour of potential exposure. A total of 1768 (9.5%) had exposure of at least one hour to an undiagnosed TB case.

Prolonged exposure was more likely for people attending the clinic for HIV care (17.3%) than for people attending for HIV testing and counselling (12%) (p < 0.001).

The researchers also looked at cumulative exposure, as patients attended the clinic a median of four times during the year. Twenty-three per cent of patients had at least three hours of exposure to an infectious TB case during the year.

The researchers say that the patient mix and experience in this clinic are likely to be typical of many HIV testing and counselling or ART clinics in sub-Saharan Africa. They draw attention to the strong recommendation from the World Health Organization that patients with suspected TB should be separated from other patients, but also note that among those with prolonged exposure (< 1 hour), almost half were exposed to people with undiagnosed TB. 

Greater attention to ventilation, waiting times and overcrowding are essential if TB transmission is to be reduced in healthcare settings, they conclude.


Mzembe T et al. Risk of Mycobacterium tuberculosis transmission in an antiretroviral therapy clinic. AIDS, advance online publication, September 2018.