118 AJTCCM VOL. 29 NO. 3 2023
ORIGINAL RESEARCH: ARTICLE
Background. ere is little evidence describing respiratory disease among 40.5 million small-scale miners worldwide.
Objectives. To describe the prevalence and clinical characteristics of adult respiratory inpatients with silicosis and silicotuberculosis in
atertiary hospital in Tanzania that serves a small-scale mining region.
Methods. In this retrospective, cross-sectional survey, patient les from admissions between 2010 and 2020 were opportunistically selected
and included if a respiratory diagnosis had been made.
Results. Of 223 patients with respiratory conditions, 32 (14.3%; 95% condence interval (CI) 10.0 - 19.6) were diagnosed with silicosis
and17 (7.6%; 95% CI 4.5 - 11.9) with silicotuberculosis. Mining was the most frequent occupation in those with silicosis (n=15/32; 46.9%)
and silicotuberculosis (n=15/17; 88.2%). Of those with silicosis or silicotuberculosis, 26/49 (53.1%) were aged <45 years.
Conclusion. Our study suggests that silicosis and silicotuberculosis are common among male and female respiratory inpatients with
occupational exposure. e study highlights the role of occupational exposures in respiratory disease in developing economies.
Keywords. Silicosis, tuberculosis, mining.
Afr J Thoracic Crit Care Med 2023;29(3):e269. https://doi.org/10.7196/AJTCCM.2023.v29i3.269
Occupational lung disease, particularly related to silica exposure, is
an overlooked but preventable cause of chronic lung disease. In 2016,
the Global Burden of Disease Study estimated 210 000 years of life
lost due to silicosis.[1] Silicosis is a direct eect of silica inhalation,
but exposure is also associated with increased risks of tuberculosis,
lung cancer and chronic obstructive pulmonary disease.[2] Miners with
silicosis have a four-fold higher risk of tuberculosis than those without
silicosis, owing to immunological reasons, damaged lung architecture
and shared environmental risks.[3]
Small-scale mining is poorly dened, but broadly encompasses
small, local companies mining borderline viable sites.[4] Small-scale
mining provides employment for an estimated 40.5 million people
worldwide, but there is little evidence to describe the burden of
respiratory diseases.[4] Of an estimated 1.5 million miners in Tanzania,
the majority work in small-scale mines. Approximately 12 000 small-
scale miners are employed at Mererani, a mining area in northern
Tanzania that is the only source of the precious stone tanzanite.
Tanzanite miners are exposed to signicantly higher levels of silica
than recommended exposure limits,[5,6] leading to concerns regarding
the miners’ respiratory health. Local experience suggests that miners
rarely wear personal protective equipment.
Kilimanjaro Christian Medical Centre (KCMC) is a large tertiary
referral hospital in Moshi, Tanzania, serving the Mererani region.
Anecdotal reports suggest that silicosis and mining-related lung
diseases are a common cause of respiratory admissions.
In this retrospective, hospital-based survey, we aimed to describe the
prevalence and clinical characteristics of silicosis and silicotuberculosis
in adult medical inpatients in KCMC.
Silicosis and silicotuberculosis among respiratory hospital
admissions: A cross-sectional surveyinnorthern Tanzania
E Dennis,1 MD; H Mussa,1 MD; M P Sanga,1 MD; P Howlett,2* MB ChB, MSc ; G Nyakunga,3* MD, MMed (Int Med)
1 Kilimanjaro Christian Medical University College, Moshi, Tanzania
2 National Heart and Lung Institute, Imperial College London, UK
3 Department of Internal Medicine, Kilimanjaro Christian Medical Centre, Moshi, Tanzania
* Joint last authors
Corresponding author: P Howlett (patrick.howlett@gmail.com)
Study synopsis
What the study adds. is retrospective, cross-sectional survey describes the prevalence of silicosis and silicotuberculosis among adult
respiratory inpatients admitted to a tertiary hospital in northern Tanzania. It is the rst study to describe the prevalence and characteristics
of respiratory inpatients with silicosis and silicotuberculosis in a small-scale mining region of Africa. A high prevalence of silicosis (14.3%)
and silicotuberculosis (7.6%) was found. Patients were oen aged <45 years, and the majority required oxygen therapy.
Implications of the ndings. e high prevalence of advanced silicosis and silicotuberculosis in miners presenting at a young age raises
concerns about high occupational silica exposures and, importantly, suggests a need for community-based research, which our team is
planning to undertake.
AJTCCM VOL. 29 NO. 3 2023 119
ORIGINAL RESEARCH: ARTICLE
Methods
Study population
A hospital-based cross-sectional survey of
patients admitted with respiratory conditions
was conducted at KCMC.
Inclusion criteria were any patient with
notes in the medical records department, aged
≥18 years, and admitted to KCMC during the
10-year period August 2010 - August 2020.
Patients were required to have a primary
lower respiratory diagnosis on discharge.
Exclusion criteria included pregnant women
and trauma.
We aimed for condence intervals of ±5%
around an estimated prevalence of 10% of
respiratory admissions with silicosis. Using
an exact binomial 95% distribution, we
calculated that a sample size of 250 respiratory
cases was needed.
Study procedures
Patient files were selected opportunistically
from the hospital records department, aiming
for a spread across all years and to reach 250
records. Primary diagnoses at discharge, as
decided by the general physician in charge of
the patient, were screened in tandem by authors
ED, HM and MPS, who were medical students
at the time of the study, with discrepancies
resolved by discussion with the general
physician (GN). Data entered electronically
using
KoboToolbox
(2021) were reviewed for
inconsistent or missing values.
Symptoms were recorded as present if noted
on admission. Demographic details, HIV
status and treatment modalities were recorded
based on presence in the notes at any point.
Occupation is routinely collected during the
admission process at KCMC, so there were no
missing values. Admission chest radiographs
are routinely performed for respiratory patients,
and findings from the radiologists’ reports
were recorded. KCMC is a tertiary hospital
with full microbiology (including GeneXpert
for tuberculosis) and laboratory services
available. Patients with a diagnosis of silicosis
currently being treated for tuberculosis were
dened as having silicotuberculosis. Numerical
data were summarised using medians and
interquartile ranges, while categorical data
were summarised using frequencies and
percentages. An exploratory multivariable
logistic regression analysis of risk factors for
respiratory failure (dened as requiring oxygen
on admission) among patients with silicosis or
silicotuberculosis was performed using a priori
variables (age, sex, mining status, smoking,
HIV status). All analyses were conducted using
Rstudio
with R version 3.6.3 (R Foundation for
Statistical Computing, Austria). Ninety-five
percent binomial exact condence intervals
(CIs) were calculated.
Ethical considerations
Ethics approval was obtained from the KCMC
Research Ethics and Review Committee.
Results
Of 223 patients with respiratory conditions
included in the study, 32 (14.3%; 95% CI
10.0 - 19.6) were diagnosed with silicosis and
a further 17 (7.6%; 95% CI 4.5 - 11.9) with
silicotuberculosis. Diagnoses of silicosis or
silicotuberculosis were most frequent in the
age group 30-44 years (n=23/49; 46.9%).
A large proportion of respiratory patients
(n=122/223; 54.7%) were current smokers.
Two-thirds of patients had an HIV status
recorded (n=135/223; 60.5%); among those
who were tested, HIV was less frequent in
those with silicosis (1/17; 5.8%) than in other
groups.
Silicosis was the third most frequent
respiratory diagnosis aer pneumonia and
tuberculosis, and silicotuberculosis the h
most frequent diagnosis (Fig.1). e most
frequent occupation in both the silicosis and
silicotuberculosis groups was mining, and
it was notable that miners presented almost
exclusively with silicosis, silicotuberculosis
or tuberculosis. Among 13 female patients
diagnosed with silicosis or silicotuberculosis,
the most frequent occupation was farming
(n=6/13; 46.2%), followed by stone work
(n=4/13; 30.8%) and mining (n=3/13; 23.1%).
Although stone work, road construction, the
steel industry and sandblasting are potentially
less frequent occupations in the general
population, they appeared relatively common
among respiratory inpatients.
Respiratory symptoms across silicosis,
silicotuberculosis and other respiratory
diagnosis groups were broadly similar
(Table 1). In both the silicosis and
silicotuberculosis groups, shortness of
breath and cough were almost universally
present, and chest pain, night sweats, fever
and weight loss were common. e frequent
presence of peripheral oedema and cyanosis
in the silicosis and silicotuberculosis groups
suggests that right heart failure was common.
In keeping with the diagnoses, radiographic
findings of fine nodularity in the upper
zones and coalescence of nodules with
hilar inltration were common in both the
Diagnosis
Pneumonia
Tuberculosis
Silicosis
COPD
Silicotuberculosis
Asthma
Interstitial lung disease
Pleural eusion
Other – infection
Other – not infection
Pulmonary oedema
Lung cancer
Chemical pneumonitis
Frequency (n)
0 10 20 30 40 50
Farming
Mining
Stone work
Road construction
Steel industry
Sand blasting
Glass manufacturing
Other
Fig.1. Bar chart of adult respiratory inpatient diagnoses by occupation (N=223). (COPD =
chronic obstructive pulmonary disease.)
120 AJTCCM VOL. 29 NO. 3 2023
ORIGINAL RESEARCH: ARTICLE
silicosis and silicotuberculosis groups, but markedly reduced in other
respiratory diagnoses.
In addition to antituberculosis medications, the majority of patients
with silicosis and silicotuberculosis received steroids (n=39/49; 79.6%)
and antibiotics (n=42/49; 85.7%). Of note, 16/17 (94.1%) of patients on
antituberculosis treatment received adjunctive steroids. e majority
(n=31/49; 63.3%) required oxygen on admission. Exploratory logistic
regression analysis found that the main risk factor for respiratory
failure among those with silicosis or silicotuberculosis was being a
miner (adjusted odds ratio 14.2; 95% CI 1.58 - 213; p=0.03).
Discussion
Although evidence suggests that silica dust exposure is high, the burden
of silicosis among small-scale miners in Tanzania is unclear. Our
retrospective, cross-sectional inpatient study found a high prevalence
of silicosis (14.3%) and silicotuberculosis (7.6%) among respiratory
inpatients in a tertiary hospital in northern Tanzania. Mining was the
main occupation in patients with silicosis and silicotuberculosis. Over
half of the patients with silicosis or silicotuberculosis presented under
the age of 45 years (53.1%), and the majority (63.3%) required oxygen
therapy.
To the best of our knowledge, there is no comparable study of
hospital silicosis or silicotuberculosis prevalence in a small-scale
mining area. In South Africa, workplace-based estimates range from
1.7% to 36.6% in current and ex-goldminers.[7-9] Although our study
may not be generalisable to the wider local mining population, the
high proportion of inpatients points to a large workforce burden of
disease. is concern is supported by high levels of silica exposure in
local mines.[5,6]
Our data suggest that a large proportion of young patients with
silicosis and silicotuberculosis present with respiratory failure. We
are mindful, however, of competing sources of bias regarding this
conclusion. On the one hand, our cases may over-represent the most
advanced and youngest cases, who are motivated to seek care in a
tertiary facility. Conversely, however, our cases may not be captured
by mine-based surveys that are prone to the healthy worker eect.
Table1. Clinical characteristics of adult respiratory inpatients with silicosis and silicotuberculosis*
Silicosis
(n=32), n (%)
Silicotuberculosis
(n=17), n (%)
Other respiratory
inpatients
(n=174), n (%)
Total
(N=223), n (%)
Age (years)
15 - 29 2 (6.2) 1 (5.9) 50 (28.7) 53 (23.8)
30 - 44 14 (43.8) 9 (52.9) 55 (31.6) 78 (35.0)
45 - 59 12 (37.5) 5 (29.4) 34 (19.5) 51 (22.9)
60 - 74 2 (6.2) 2 (11.8) 24 (13.8) 28 (12.6)
75 - 89 2 (6.2) 0 11 (6.3) 13 (5.8)
Gender
Female 11 (34.4) 2 (11.8) 48 (27.6) 61 (27.4)
Male 21 (65.6) 15 (88.2) 126 (72.4) 162 (72.6)
HIV status
Negative 16 (50.0) 10 (58.8) 84 (48.3) 110 (49.3)
Positive 1 (3.1) 2 (11.8) 22 (12.6) 25 (11.2)
Missing or not recorded 15 (46.9) 5 (29.4) 68 (39.1) 88 (39.5)
Smoker
Ye s 16 (50.0) 4 (23.5) 93 (53.4) 123 (55.2)
No 16 (50.0) 13 (76.5) 81 (46.6) 100 (44.8)
Symptoms
Shortness of breath 31 (96.9) 17 (100) 157 (90.2) 205 (91.9)
Cough 32 (100) 17 (100) 170 (97.7) 219 (98.2)
Wheeze 19 (59.4) 6 (35.3) 73 (42.0) 98 (43.9)
Weight loss 23 (71.9) 13 (76.5) 89 (51.1) 125 (56.1)
Chest pain 31 (96.9) 15 (88.2) 153 (87.9) 199 (89.2)
Fever 15 (46.9) 9 (52.9) 94 (54.0) 118 (52.9)
Night sweats 26 (81.2) 14 (82.4) 88 (50.6) 128 (57.4)
Cyanosis 13 (40.6) 3 (17.6) 48 (27.6) 64 (28.7)
Lower limb oedema 12 (37.5) 8 (47.1) 45 (25.9) 65 (29.1)
Radiographic ndings
Fine nodularity in the upper zone of the lungs 20 (62.5) 11 (64.7) 13 (7.5) 44 (19.7)
Coalesced nodules with hilar inltration 7 (21.9) 3 (17.6) 6 (3.4) 16 (7.2)
Miliary patterns 3 (9.4) 2 (11.8) 27 (15.5) 32 (14.3)
Other ndings 2 (8.7) 1 (5.9) 128 (73.6) 131 (58.7)
*No variables had missing values except for HIV status.
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Nevertheless, our ndings raise the concern that individuals from the
local area with high silica exposure[5,6] may be presenting at younger ages
than expected with advanced disease.
Elementary occupations (those involving routine tasks, oen hand-
held tools and a degree of physical eort) in Tanzania represented 10.9%
of all employment in 2014.[10] e comparatively high frequency of stone
work, road construction, steel industry and sandblasting workers in our
study suggests that these may be over-represented among inpatients
with respiratory disease. We found that a third (34.4%) of patients with
silicosis were women, in keeping with estimates that 40 - 50% of small-
scale miners are women.[11]
Importantly, there appears to be a missed opportunity for HIV testing,
with 39.5% of
patients having no HIV status recorded. Rates of smoking
also appear very high among both silicosis-related and non-silicosis-
related diseases (54.7%), highlighting the vital role of anti-tobacco
policies. e clinical and radiological similarities between silicosis and
silicotuberculosis highlight the practical challenges of diagnosis.
Our study has significant limitations. First, we did not have a
standardised method for selecting patient notes, meaning that our
sample may not be representative of the underlying population. Second,
as the hospital charges user fees it is possible that the prevalence of
miners is over- or under-estimated based on their ability to pay for their
care, relative to other patients. ird, the infrequent use of advanced
diagnostics such as bronchoscopy and chest computed tomography
means there is a risk of misclassication bias regarding diagnosis.
Finally, we did not record patients’ residence or their location of work.
While the largest small-scale mining population is in the Mererani
region, there are other small-scale and large-scale mining locations in
the catchment area of KCMC with high exposures.
[6]
Conclusions
Our hospital-based study found a high prevalence of young
inpatients with silicosis and silicotuberculosis, who oen presented
with respiratory failure. is nding raises concerns regarding high
occupational dust exposure and supports workplace studies of silica-
related disease in exposed industries, such as artisanal and small-scale
mining, in northern Tanzania. More broadly, the ndings highlight
the important role of occupational exposures in the growing burden
of chronic lung diseases in developing economies.
Declaration. e research for this study was done in partial fullment
of the requirements for ED, HM and MPS’s MD degrees at Kilimanjaro
Christian Medical University College, Tanzania.
Acknowledgements. We would like to thank the hospital records and
radiology departments at KCMC for their assistance with this project.
Author contributions. HM, ED, MPS: conceptualisation, methodology,
project administration, data collection, writing – original dra preparation.
PH: data curation, formal analysis, visualisation, writing – original dra
preparation. GN: supervision, writing – review and editing.
Funding.None.
Conicts of interest.None.
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Submitted 12 July 2022. Accepted 28 May 2023. Published 19 September 2023.
