Open windows cut risk of minibus TB

Public bus
Minibus picking up passenger as it drives along. Copyright: AMISOM Photo / Omar Abdisalan, Public domain

Speed read

  • Sub-Saharan Africa has 16 of the 30 countries the WHO considers as having high TB burden
  • New study finds that opening windows of minibus taxis could help cut TB spread
  • Policymakers should enact adequate policies to protect the health of passengers

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[CAPE TOWN] Two sets of open windows in the front and the back of a minibus taxi could provide enough air to reduce the risk of tuberculosis transmission, a study conducted in South Africa suggests.
In 2016, the WHO Africa region accounted for 25 per cent of 10.4 million new cases of TB globally, according to the 2017 WHO TB report. Of the 30 high-burden countries, Sub-Saharan Africa alone has 16 of the countries including Nigeria and South Africa.
The high TB burden in South Africa led researchers from the country’s University of Cape Town to study whether minibus taxis could provide sufficient ventilation to mitigate the potential spread of TB from undiagnosed and untreated passengers.

“The high passenger occupancy seen in taxis combined with unguided open window policies means there is a danger of airborne infectious diseases”

Munyaradzi Matose, University of Cape Town

“The high passenger occupancy seen in taxis combined with unguided open window policies means there is a danger of airborne infectious diseases such as TB being spread unknowingly to passengers,” says Munyaradzi Matose, a biomedical engineer at the University of Cape Town, South Africa, and lead researcher of the study published in the September and October issue of the South African Journal of Science.

Previous studies conducted in countries including Peru and Tanzania showed high chances of contracting TB in public transportation.

But Matose says their study focussed on particular window configurations that could give high ventilation rates to cut TB spread.
Using a single temperature data logger, researchers observed the window openings of a 16-seater Toyota minibus, and assessed passenger occupancy and taxi speeds on 23 journeys taken in the minibus in and around Cape Town in June-July 2015.

Researchers tested six window configurations – two in front, middle two and back two windows each opened at the same time as the taxi drove at different speeds: 40, 80 and 100 kilometres per hour.
The ventilation of airborne disease precaution rooms was compared with the ventilation achieved by the different window configurations.
According to the study, the best configuration for air ventilation was to have the front and back pairs of windows open at all speeds, with a minimum ventilation rate of 218 litres per second measured at 40 kilometres per hour, exceeding that recommended by the WHO for an airborne disease precaution room.
The WHO recommends that ventilation in general wards and outpatient departments be at least 60 litres per second for each patient and that new health-care facilities precaution rooms should have a ventilation rate of 80 litres per second for each patient.
The results were that two windows could provide enough ventilation per person as per WHO recommendations, Matose tells SciDev.Net.

He says this study can be replicated elsewhere using a carbon dioxide sensor with data logging capacities. The same experiments could also be carried out on other public transport such as buses and trains, which in South Africa often have similar high passenger occupancy rates.

But he warns that despite the ventilation capabilities achieved in the study, passengers might not tolerate the fully open windows whilst travelling at speed because of the discomfort caused by temperature or weather changes.

Given that taxis are often congested or overloaded during peak hour commuting journeys, vehicles can be designed to have improved air circulation, Matose says.

He further recommends minibus taxi operators and passengers to keep windows open particularly in fully occupied vehicle to stop the spread of TB in South Africa where the vehicles are the mainstay of daily public transport.

Francis Mhimbira, infectious disease epidemiologist at Ifakara Health Institute, Tanzania, says that the study is important as it highlights importance of TB infection control in areas where possible transmission of TB can occur.
“Because TB is airborne any means to improve cross ventilations in mini-busses should be encouraged,” explains Mhimbira, adding that if a minibus taxi passenger has TB, then increasing ventilation could reduce the risk of infecting others.
Mhimbira says that the key message from the study is raising awareness of TB spread through public transportation.  
Matose tells policymakers to use the study’s findings to enact policies that will help the public to benefit from open windows during journeys.

“Make a definitive policy that requires all new models of taxis to come equipped with the capacity to reduce airborne infectious disease spread,” he says.
This piece was produced by SciDev.Net’s Sub-Saharan Africa English desk.


Munyaradzi Matose and others Natural ventilation as a means of airborne tuberculosis infection control in minibus taxis (South African Journal of Science, September-October, 2019