Outbreak of Severe Histoplasmosis Among Tunnel Workers—Dominican Republic, 2015
Outbreak of Severe Histoplasmosis Among Tunnel Workers-Dominican Republic, 2015
Paige A. Armstrong 2
John D. Beard 1 6
Luis Bonilla 0
Nelson Arboleda 0
Mark D. Lindsley 7
Sae-Rom Chae 5
Delia Castillo 4
Ramona Nuñez 4
Tom Chiller 7
Marie A. de Perio 3
Raquel Pimentel 4
Snigdha Vallabhaneni 7
0 Centers for Disease Control and Prevention , Santo Domingo , Dominican Republic
1 Epidemic Intelligence Service, Industrywide Studies Branch, Division of Surveillance, Hazard Evaluations and Field Studies, National Institute for Occupational Safety and Health (NIOSH) , Cincinnati, Ohio , USA
2 Epidemic Intelligence Service, Mycotic Diseases Branch, Division of Foodborne , Waterborne, and Environmental Diseases (DFWED) , National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Centers for Disease Control and Prevention (CDC) , Atlanta , Georgia
3 Hazard Evaluations and Technical Assistance Branch, Division of Surveillance, Hazard Evaluations and Field Studies , NIOSH, Cincinnati, Ohio , USA
4 Dirección General de Epidemiología , Santo Domingo , Dominican Republic
5 Epidemic Intelligence Service , Global Water, DFWED, NCEZID, CDC, Atlanta , Georgia
6 Present affiliation: Department of Health Science, College of Life Sciences, Brigham Young University , Provo, Utah. Rd NE, MS C-09, Atlanta, GA 30329 , USA
7 Mycotic Diseases Branch
Background. Histoplasmosis is a fungal infection associated with exposure to bat guano. An outbreak of an unknown severe febrile illness occurred among tunnel workers in the Dominican Republic, and resulted in several deaths. We conducted an investigation to confirm etiology and recommend control measures. Methods. A case was defined as fever and ≥2 symptoms consistent with histoplasmosis in a tunnel worker, July-September 2015. We interviewed workers and family members, reviewed medical records, tested serum and urine for Histoplasma antigen/antibody, and conducted a cohort study to identify risk factors for histoplasmosis and severe infection (intensive care). Results. A crew of 36 male workers removed large amounts of bat guano from tunnels without respiratory protection for a median of 24 days per worker (range, 1-25 days). Median age was 32 years (range, 18-62 years); none were immunocompromised. Thirty (83%) workers had illness that met the case definition, of whom 28 (93%) were hospitalized, 9 (30%) required intensive care, 6 (20%) required intubation, and 3 (10%) died. The median time from symptom onset to antifungal treatment was 6 days (range, 1-11 days). Twenty-two of 34 (65%) workers had laboratory evidence of infection. Conclusions. Severe illnesses and death likely resulted from exposure to large inocula of Histoplasma capsulatum spores in an enclosed space, lack of respiratory protection, and delay in recognition and treatment. Clinician education about histoplasmosis, improved laboratory capacity to diagnose fungal infections, and occupational health guidance to protect workers against endemic fungi are recommended in the Dominican Republic.
Histoplasma capsulatum, the causative agent in
histoplasmosis, is often found in association with bird or bat droppings [
Histoplasma capsulatum is present throughout the Americas
and the Caribbean. Exposure to H. capsulatum typically occurs
by inhalation of fungal spores, specifically the microconidia,
following disruption of soil or other contaminated material.
Once at body temperature (37°C), it transforms into the yeast
phase. The average incubation period is 1–3 weeks, and
clinical manifestations can range from asymptomatic infection to
severe, disseminated disease [
]. Acute pulmonary
histoplasmosis is the most common symptomatic manifestation and is
often self-limited, especially among healthy persons.
On 16 September 2015, the Dominican Republic Ministry of
Health (DR MoH) requested assistance from the US Centers for
Disease Control and Prevention (CDC) with the investigation of
an unknown severe febrile illness among several male tunnel
workers. All men were members of a work crew tasked with removing
bat guano from access tunnels to a hydroelectric dam. Workers
were initially treated for leptospirosis, which is endemic to the area.
Histoplasmosis was later considered when examination of one
patient’s bronchoalveolar lavage (BAL) specimen demonstrated
yeast cells, consistent with histoplasmosis; however, there was no
local laboratory capacity to confirm the diagnosis. Three men had
died and 25 others were hospitalized. Although histoplasmosis is
endemic to the Americas, including other Caribbean islands such
as Puerto Rico and Jamaica, cases had never been diagnosed in the
]. Local physicians were unfamiliar with diagnosis and
management of histoplasmosis. CDC and the DR MoH investigated to
confirm the etiology of the outbreak, elucidate clinical and
occupational risk factors for histoplasmosis and severe disease, assess
treatment outcomes, and identify control measures.
Descriptive Epidemiology and Cohort Study
We defined a case of histoplasmosis as fever and ≥2 symptoms
(chills, night sweats, weakness, joint pain, cough, headache,
generalized malaise, dyspnea, myalgias, difficulty breathing,
diarrhea, and vomiting) in a person who worked in the tunnels
during 30 July–2 September 2015; this time period included all
work performed on the tunnels. We reviewed company payroll
records to identify all persons who had worked in the tunnels
during that time period and interviewed workers to identify any
additional persons exposed to the tunnels who may not have
been on the official company records (eg, temporary substitutes
for regular workers).
We interviewed tunnel workers in person in Spanish using a
standardized questionnaire. For the 3 workers already deceased
at the time of the interview, we spoke with an immediate family
member. Worker interviews addressed demographic
characteristics, underlying medical conditions, general information
about the tunnels, number of days spent in the tunnels, tasks
performed, and use of personal protective equipment.
We reviewed medical records from the local hospital where
workers were initially hospitalized, and regional hospitals,
where they were later transferred for care, using a standardized
case report form that included clinical information, details of
the hospital stay, treatment, and outcome.
We conducted a cohort study to identify risk factors for
developing histoplasmosis and severe disease (defined as admission to
the intensive care unit [ICU]). The cohort included all workers
exposed to the tunnels during 30 July–2 September 2015.
We collected serum and urine samples from tunnel workers
and sent them to the CDC Mycotic Diseases Branch laboratory
(Atlanta, Georgia) for analysis. Environmental sampling is not
routinely performed and given the volume of guano involved
in this outbreak, processing of environmental samples was not
feasible. Histoplasma capsulatum antigen detection was
performed on both urine and serum samples using an enzyme
immunoassay (EIA) employing Histoplasma monoclonal
analyte-specific reagents (IMMY, Norman, Oklahoma), with a
cutoff value of ≥0.5 ng/mL for a positive result. Before performing
the assay, we treated serum with pronase at 56°C for 30 minutes
followed by boiling for 5 minutes. We tested urine undiluted.
Optical density EIA results were analyzed against a 7-point
standard curve to provide a quantitative result [
]. EIA was
chosen over other molecular methods as it can be performed on
specimens that do not require invasive collection procedures,
such as BAL or tissue biopsy. We performed qualitative
H. capsulatum antibody detection using immunodiffusion on serum
samples. In the outbreak setting, we considered an M band
sufficient to conclude a positive result.
We calculated medians and ranges for continuous variables,
and frequencies and percentages for categorical variables.
We evaluated unadjusted associations between demographic,
occupational, exposure, and clinical variables using the
outcomes of histoplasmosis and severe disease. We used exact
logistic regression models to estimate exact odds ratios and
exact 95% confidence intervals (CIs). We assumed linear
relationships for continuous variables, but categorized them with
category boundaries set either at the median or quartiles when
the Akaike information criterion indicated that a linear term
was not the best fit [
]. We considered exact 2-sided P values
of ≤.05 to be statistically significant. Due to the small size of our
study, we also considered P values between .05 and .1 to be
“borderline significant.” Statistical analyses were performed with
SAS version 9.3 software (SAS Institute, Cary, North Carolina).
A local ethics committee in the DR and designated ethics
officers at CDC determined that this was an emergency public
health investigation and did not meet criteria for research.
Background on Tunnel Work
The dam was constructed in 1972 and provides hydroelectric
energy to most of the surrounding communities. This
embankment dam had 5 tunnels, each approximately 1–2 km long,
which allow access to the dam for inspection and maintenance.
Tunnel entrances were small (approximately 3 m wide and tall)
(Figure 1). The tunnels lacked ventilation or illumination and
were inhabited by large bat colonies. Bat guano up to 1 m deep
had accumulated since the tunnels were last accessed
approximately 30 years ago.
A private company was contracted to clean the tunnels and
recruited workers informally in a nearby town center. A total of
36 workers were exposed to the tunnels during July–September.
Each worker was provided with a pair of knee-high rubber boots,
a hard hat with an attached personal headlamp, and a shovel.
Additionally, some workers received loose-fitting paper surgical
masks. Workers were responsible for filling wheelbarrows with
bat guano, transporting it outside, and depositing it
immediately near the tunnel entrance. They worked for 3–4 hours daily,
5 days per week, usually in the mornings. Work cleaning 2 of
the tunnels began 30 July 30 and stopped 2 September, when a
number of workers became ill.
All workers were male and the median age was 32 years (range,
18–62 years); 5 (15%) reported having asthma, 15 (43%) were
current cigarette smokers, and 12 (39%) used illicit drugs
(Table 1). Fifteen workers (43%) reported shoveling guano as
their sole task, 5 (14%) reported only transporting the
wheelbarrows containing guano, 11 (31%) engaged in both tasks, 3
(9%) supervised the work of others, and 1 (3%) performed other
work (eg, holding a light). Ten (29%) workers worked in tunnel
1 only, 7 (20%) worked in tunnel 2 only, and 18 (51%) worked
in both tunnels (4 workers worked 1–4 days in a third tunnel
in addition to working in tunnels 1, 2, or both, but we did not
consider the third tunnel in analyses because it could not have
accounted for the large number of workers who became ill).
The median number of days per worker spent in the tunnels
was 24 (range, 1–25 days). Workers reported oppressive heat
and difficulty breathing inside the tunnels while wearing the
masks. Sixteen (48%) workers never used the masks, 14 (42%)
used them sometimes, and 3 (9%) reported using them always
The first ill worker presented to the local hospital on 28 August
with an unknown febrile illness (Figure 2). By 4 September, 14
workers had been admitted to the local hospital. Leptospirosis
was initially suspected as the cause of the outbreak because it is
endemic to the region. However, the workers did not improve
with penicillin, the treatment for leptospirosis. Physicians noted
the common exposure to tunnel work among the admitted
patients and reported the illnesses to the local health
authorities. On 8 September, all 19 workers who had been admitted to
the local hospital were transferred to regional hospitals, where
a higher level of care was available to manage their unknown
illness. Two of the 19 (11%) workers transferred from the local
hospital to regional facilities required intubation within 1 day
of arrival. At one regional facility, an astute physician, who
had treated cases of histoplasmosis while training in Mexico,
suggested the diagnosis of histoplasmosis given its association
with exposure to bat guano. The same day, a pathologist noted
yeast cells, suggestive of H. capsulatum by microscopy on a BAL
Thirty of the 36 (83%) exposed workers had illnesses that met
the case definition. Symptom onset ranged between 21 August
and 11 September 2015 (Figure 2). Twenty-eight (93%)
workers were hospitalized, 9 (30%) required ICU admission, 6 (20%)
were intubated, and 3 (10%) died (Table 2). The 3 workers who
died were 21–36 years of age, had no known medical
comorbidities, and were nonsmokers. All 3 received voriconazole and
Nine of 30 (30%) case patients underwent bronchoscopy; 7
of these had BAL samples collected and 6 (86%) had BAL
cultures positive for bacteria, consistent with ventilator-associated
pneumonia. These samples were not available for further
evaluation for H. capsulatum (Table 2).
Nineteen (68%) case patients had leukocytosis (white blood
cell count >12 × 109/L) and 10 (36%) had aspartate
aminotransferase or alanine aminotransferase >120 U/L. Human
immunodeficiency virus testing was performed for 15 (50%) case
patients, and none were positive. Testing for leptospirosis, the
original suspected pathogen, was performed for 23 (77%) case
patients, and none were positive (Table 2).
Twenty-eight (93%) case patients received an antifungal,
and the median time from symptom onset to first antifungal
treatment was 6 days (range, 0–11 days). Voriconazole was the
first antifungal administered to 16 (62% of those with data)
case patients and 17 (61%) received >1 antifungal (not shown).
Overall, 22 (79%) case patients received voriconazole, 14 (50%)
received itraconazole, 9 (33%) received fluconazole, and 8
(29%) received amphotericin B during their treatment course.
Twenty-six (87%) case patients received corticosteroids and 4
Date of Symptom Onset
(16%) received corticosteroids at least 1 day before treatment
with antifungals (Table 2).
Thirty-four of the 36 exposed workers provided samples; we
obtained 34 unique serum and 29 unique urine specimens. Urine
and serum were available for 28 workers. Time from symptom
onset to collection of specimen ranged from 5 to 33 days, with
a median of 14 days. Eighteen (53%) serum and 13 (45%) urine
samples were positive for H. capsulatum antigen. Additionally,
immunodiffusion was performed on 31 serum samples, and 11
(35%) were positive. In total, 22 of the 34 (65%) workers tested
had laboratory evidence of H. capsulatum infection.
None of the variables examined in the cohort
analysis—including age, presence of comorbidities, type of work, tunnel of
work, days worked in tunnels, personal protective equipment
use, days from symptom onset to antifungal treatment (ICU
admission only), symptoms (ICU admission only), and laboratory
results (ICU admission only)—were significantly associated
with histoplasmosis or severe disease (ICU admission) (Tables
3 and 4; and Supplementary Table 1). However, days worked in
tunnels (P = .06) and difficulty breathing (P = .07) had
borderline significant positive associations with severe disease.
This is the first report of an outbreak of histoplasmosis in
the DR. Histoplasma capsulatum is endemic to the Caribbean
region, and outbreaks have been reported throughout Latin
]. Sporadic cases of histoplasmosis attributed
to exposure in the DR have been diagnosed in travelers
returning to their countries of origin . Clinicians in the DR were
largely unfamiliar with histoplasmosis and laboratories did
not have the capacity to definitively diagnose the disease. It
is possible that there have been previous cases and outbreaks
of histoplasmosis in the DR that have gone unrecognized as
the illness is often self-limited. The high mortality in a young
healthy population likely brought more attention to this
outbreak, and the investigation led to the confirmation of
histoplasmosis in the DR.
Outbreaks of histoplasmosis tend to involve small numbers
of people and fatalities are rare, even in resource-poor settings
]. Several factors may have contributed to the high
proportion of hospitalizations and deaths observed in this outbreak.
Although local physicians and public health authorities quickly
recognized that the ill workers had been exposed to tunnels,
recognition of histoplasmosis and initiation of antifungal
treatment were delayed. Furthermore, amphotericin B, the
recommended treatment for severe pulmonary histoplasmosis, was
not administered in the majority of cases despite
decompensation, and when administered, it was delayed [
]. The causes
of this delay were likely multifactorial, and due to both
unfamiliarity of physicians with guidelines and lack of access to the
medication. Paucity of serologic or urine diagnostic capacity
likely also contributed to the delay in definitive diagnosis and
subsequent treatment. Aside from the delayed diagnosis and
treatment, probable exposure to high H. capsulatum inocula
in the tunnels, coupled with poor ventilation and inadequate
occupational precautions, contributed to the outbreak’s severity.
Histoplasmosis in the Dominican Republic • CID 2018:66 (15 May) • 1553
Abbreviations: ALT, alanine aminotransferase; AST, aspartate aminotransferase; BAL, bronchoalveolar lavage; CT, computed tomography; CXR, chest radiograph; HIV, human
immunodeficiency virus; WBC, white blood cell count.
aCategory boundaries set at the quartiles among all workers who met the case definition and who had any antifungal.
Earlier diagnosis and treatment of histoplasmosis, combined
with appropriate occupational precautions, might have
prevented the 3 deaths observed in this outbreak.
A greater number of days spent in the tunnels was
associated with increased risk of severe disease, although this
association was only borderline statistically significant, likely due to
the small sample size. It is known that H. capsulatum can exist
in “hotspots,” or pockets within the environment. When these
pockets are disrupted, large amounts of spores can be released
into the air [
]. We suspect that such events occurred during
this outbreak, exposing workers to large inocula within short
periods of time. Workers’ proximity to these “hotspots” rather
than their cumulative time spent in the tunnels may have
determined their risk of acquiring histoplasmosis. This hypothesis is
1554 • CID 2018:66 (15 May) • Armstrong et al
supported by the clustering of symptom onset during a 2-week
period rather than over the entire duration of the tunnel work.
Increased education and awareness of histoplasmosis among
clinicians is needed to respond to cases and future outbreaks
in the DR, as early treatment with an appropriate antifungal
can reduce morbidity and mortality [
]. As elsewhere in Latin
America and the Caribbean, histoplasmosis is likely an
important cause of disease. In fact, we suspect that had
convalescent testing been performed, we would have detected exposure
and antibody response in even more of the tunnel workers.
In the acute setting, antibodies may not yet have formed and
antigen-based testing can be falsely negative. Unfortunately,
we were unable to collect convalescent sera in this outbreak
]. Enhanced availability of histoplasmosis
diagnostics may help uncover an unrecognized burden of illness.
Historically, antibody and antigen testing has been performed
by only a limited number of laboratories worldwide. Newer
diagnostic technologies, such as point-of-care loop-mediated
isothermal amplification or lateral flow assays, could facilitate
rapid detection and treatment, especially in resource-limited
Because tunnels involved in this outbreak could not be closed
for access, as they are needed for continued maintenance of the
dam, using the occupational health and safety hierarchy of
controls will be important for preventing additional illnesses [
Development of a site safety plan is an important step in
minimizing exposure, and provides direction for continued access
and work in the tunnels. Additional methods, such as
moistening material prior to translocation, can reduce dust generation
and spore dispersal [
]. Given the likely spore burden present
in the guano, when removed it should be treated as
biohazard waste to minimize further disease [
]. Worker training is
another key component and should address heat exhaustion,
health risk communication, appropriate use of personal
protective equipment, and compliance with occupational health and
environmental safety recommendations [
]. The US National
Institute for Occupational Safety and Health (NIOSH) has
developed recommendations for the prevention of histoplasmosis in
occupational settings [
]. NIOSH considers disposable N95
respirators to be the lowest acceptable level of protection needed
when working in areas with the potential for H. capsulatum
]. In this outbreak, the tunnel workers were
provided with paper surgical masks that were not consistently worn
and would not have provided adequate protection.
Applying the safe work practices discussed above to the
setting of this outbreak may be challenging given the tropical
climate and limited resources. The tunnels are poorly ventilated
and hot, likely limiting extended use of any type of respirator;
furthermore, personal protective equipment can be costly.
Specialists, such as an industrial hygienist, could help determine
Histoplasmosis in the Dominican Republic • CID 2018:66 (15 May) • 1555
Data are presented as No. (%) unless otherwise indicated.
Abbreviations: CI, confidence interval, ICU, intensive care unit.
aCategory boundary set at the median among all workers.
bMedian unbiased estimate.
cAmong only the 28 workers who had received any antifungal.
dCategory boundaries set at the quartiles among all workers who met the case definition and who had received any antifungal.
the most appropriate and feasible options (see Supplementary
Materials for full details).
Our study had several limitations that may have interfered
with our ability to detect associations. First, we interviewed
workers several weeks after work in the tunnels concluded,
potentially introducing recall bias. Second, it is conceivable that
given the widespread medical evaluation of exposed workers,
some may have overreported symptoms. This could increase
the number of cases detected, biasing the risk ratio toward the
null. Finally, the small sample size limited our ability to adjust
for potential confounders or to find risk factors associated with
developing histoplasmosis or severe disease.
This outbreak adds to evidence that histoplasmosis is
underdiagnosed in Latin America and the Caribbean [
Increased awareness of the disease among clinicians and
public health officials, improved diagnostic capacity, and access to
antifungals is essential in helping to prevent severe illness and
death. Occupational health precautions during higher-risk
1556 • CID 2018:66 (15 May) • Armstrong et al
activities, particularly those involving disturbances to bird and
bat guano, could reduce worker exposure to H. capsulatum.
Because workers are often at higher risk of exposure than the
general population, the identification of high-risk
environments as well as the implementation of appropriate engineering
and administrative controls and adequate personal protective
equipment may help to prevent similar outbreaks in the future.
Supplementary materials are available at Clinical Infectious Diseases online.
Consisting of data provided by the authors to benefit the reader, the posted
materials are not copyedited and are the sole responsibility of the authors,
so questions or comments should be addressed to the corresponding author.
Disclaimer. The findings and the conclusions in this report are those
of the authors and do not necessarily represent the views of the Centers
for Disease Control and Prevention (CDC) or the National Institute for
Occupational Safety and Health (NIOSH).
Financial support. This work was supported by the CDC and NIOSH.
Potential conflicts of interest. All authors: No reported conflicts of
interest. All authors have submitted the ICMJE Form for Disclosure of
Potential Conflicts of Interest. Conflicts that the editors consider relevant to
the content of the manuscript have been disclosed.
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