Tuberculosis is the world's leading infectious cause of death, claiming at least 500 000
more lives than COVID-19 in 2020.
1
The COVID-19 pandemic has irrevocably damaged tuberculosis care and will cause an
excess 6 million tuberculosis deaths by 2025. How can tuberculosis control possibly
benefit from the varied and flawed public health response to COVID-19?
Early and widespread face-mask wearing could have prevented the outbreak of severe
acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from becoming a pandemic.
2
Face masks were initially recommended for outward protection to prevent transmission
from infectious individuals. Following a review that also showed inward protection
(ie, for the wearer), WHO recommended use of face masks by the public.
3
Historically, public mask-wearing to prevent tuberculosis transmission met scepticism
and low uptake due to stigma, restricted access, discomfort, and perceived liberty
deprivation—similar barriers to those faced by condom uptake for HIV prevention.
4
However, whereas condom acceptance improved, mask adoption to reduce tuberculosis
transmission stagnated, even among patients with a positive test result, and mask
wearing was often seen as an embarrassing public declaration of ill health. In a pre-COVID-19
survey we did in 100 patients with drug-resistant tuberculosis in Cape Town, South
Africa, who were likely to be infectious, only 2% reported wearing surgical masks
in shops. This proportion was similar to that of patients who reported wearing masks
on public transport.
The pandemic could have created a momentum of mask acceptance beneficial for tuberculosis
control. For example, in South Africa, public face masks have been mandatory for more
than 6 months. If acceptance of masks can be maintained, it could be a game changer
for tuberculosis control in high-burden countries—provided there is evidence that
the masks used to protect from SARS-CoV-2 also reduce the infectiousness of tuberculosis,
particularly the non-conventional forms such as cloth masks.
Unlike SARS-CoV-2, Mycobacterium tuberculosis transmission is almost exclusively airborne.
When wearing a mask, air can still pass through the gaps between mask and face.
5
Although minimising these gaps is crucial for inward protection, Richard Riley, who
confirmed the airborne nature of M tuberculosis transmission, is unconcerned about
these leaks from an outward-protection perspective. He believes even simple cough
etiquette should be effective because organisms leaving the mouth are still in droplets,
which have not evaporated to droplet nuclei and are still large enough to impinge
on an obstructing surface, such as the hand, and remain there.
6
Data supporting Riley's view are sparse, but wearing a mask should act as a form of
cough etiquette that is at least as effective as hands are.
In 2015, we seated patients with cystic fibrosis inside large cylindrical tanks and
mixed air homogeneously to capture airborne particles, including those that escape
through mask gaps. During coughing, surgical masks reduced airborne, culturable Pseudomonas
aeruginosa by 88% (95% CI 81–96).
7
M tuberculosis and P aeruginosa are similar in size but both are much larger than
viruses. However, mask–pathogen interactions depend mainly on particle and not pathogen
size (ie, the particles carrying viruses or bacteria might have similar sizes).
8
In 2018, Michelle Wood and colleagues validated our P aeruginosa findings with another
aerosol platform.
9
Few studies have directly examined the effect of surgical masks on the infectiousness
of tuberculosis; Ashwin Dharmadhikari and colleagues reported that 56% (95% CI 33–71)
fewer guinea pigs were infected when they were exposed to air from inpatients on days
those inpatients were encouraged to wear masks.
10
To help policy makers decide whether public face-mask usage should be maintained for
tuberculosis control as the COVID-19 pandemic wanes, more data are needed on the effect
of masks on reducing the infectiousness of patients with tuberculosis. In July, 2018,
we started recruiting patients with tuberculosis in Cape Town to study the effect
of face masks (including non-conventional forms) using our aerosol platform. Pilot
results, obtained before the study was paused because of the pandemic response measures,
indicated that surgical masks are effective and that non-conventional and less stigmatising
mask designs (eg, neck gaiters) and cheaper forms (eg, paper masks) are efficacious.
It will take more than a year until conclusive data are published. However, public
mask-wearing fatigue, unless it is urgently addressed, could close this rare window
afforded by the COVID-19 response.
Mathematical modelling of the COVID-19 and tuberculosis epidemics in China, India,
and South Africa, which did not factor in the effect of masks deployed for SARS-CoV-2
on tuberculosis transmission, suggests that reducing contacts by physical distancing
would lead to population-level reductions in tuberculosis transmission and incidence,
but also that these benefits would be offset by health service disruptions, resulting
in net increases in tuberculosis cases and deaths.
11
Hence, with the restoration of critical tuberculosis health-care services and economic
activity as part of the post-COVID-19 recovery, policies for sustained mask-wearing
could help turn the tide against tuberculosis. However, this proposal will require
formal modelling.
Notably, the widespread public face-mask usage for SARS-CoV-2 partly stemmed from
concerns about presymptomatic and asymptomatic transmission. Half of the prevalent
cases of bacteriologically confirmed tuberculosis are probably subclinical (ie, symptom
screen is negative).
12
Whether such patients can transmit tuberculosis is not yet confirmed but is probably
the case: a study in symptomatic patients found those with lower symptom scores to
be more infectious.
13
Therefore, the rationale for public mask usage against presymptomatic and asymptomatic
spread of SARS-CoV-2 might also apply to tuberculosis spread. Another consideration
is that improper mask hygiene and fomite risk, which could be downsides of mask usage
for SARS-CoV-2, are not a concern for tuberculosis due to its almost exclusively airborne
transmission route.
Although face masks vary in breathability and filtration characteristics, a good-quality
cloth mask could be as effective as a surgical mask,14, 15 including for tuberculosis.
Tuberculosis-endemic countries need to decide who should wear masks, and the times
or places they should wear them (figure
). As a first step, cloth masks should be available outside of clinics for patients
with tuberculosis awaiting diagnostic investigation and, in high-burden settings,
for people with tuberculosis risk factors. Population-level mask-wearing should tackle
any re-emergence of stigma. Because airborne particles disappear quickly outside,
face masks should be prioritised for indoor use.
Figure
Proposed face-mask recommendations that build on COVID-19 policies in tuberculosis-endemic
countries
Suggestions and explanations are listed for who should wear masks, when they should
wear them, where they should wear them, and the type of mask that should be considered.
In conclusion, although tuberculosis care is critically weakened by the COVID-19 pandemic,
there is an unprecedented opportunity to throw masks into the fight against the long-standing
tuberculosis pandemic. Although available data are sparse, which is something we are
addressing, they suggest face masks, including non-conventional forms, can reduce
the infectiousness of patients with tuberculosis. High tuberculosis transmission settings
must retain mask-wearing as the COVID-19 pandemic wanes and pivot and protect the
widespread public acceptance of face masks towards tuberculosis control.
© 2021 Garo/Phanie/Science Photo Library
2021
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