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Patterns in Descriptive Epidemiological Variables in Blastomycosis Outbreaks
By: Bill Luebke
Epidemiology
Abstract
Blastomycosis is a disease caused by the dimorphic fungus called Blastomyces dermatitidis. It exists in
mold form and is found in decaying vegetation, animal and bird excrement, and organic debris. There
are many small outbreaks of blastomycosis throughout the United States, Mexico, and Canada. I
completed a cross-sectional study by researching specific case studies and analyzed these studies to find
any descriptive epidemiological patterns between the outbreaks: age, race, gender, and location. Men
aged 40 years old, of any race have a higher incidence rate to blastomycosis. 60% of males in the case
studies were more likely to get blastomycosis than females. The median age for all case studies was
40.9 years of age. There was a very wide range of patients that were diagnosed with blastomycosis;
from 4 months to 95 years of age. A correlation between race and blastomycosis was not found
because there was insufficient information provided to make any comparisons. Most common
incidences occurred in rural, wooded, and riverbed areas.
Description of Disease
Blastomycosis is a disease caused by the dimorphic fungus called Blastomyces dermatitidis. It exists in
mold form and is found in decaying vegetation, animal and bird excrement, and organic debris.
According to the Canadian Material Safety Data sheet (2010), “the infection develops when conidia of
Blastomyces dermatitidis are aerosolized from soil.” The spores are either inhaled or planted into the
skin of a susceptible human or animal at 25 degrees Celsius. The warmer temperature of the host
transforms the mold into yeast once it reaches 37 degrees Celsius. The yeast may continue to colonize
the lungs and cause adult respiratory distress syndrome (ARDS) and/or obstructive lung disease. It may
spread into the bloodstream and cause damage to other parts of the body, skin, bones, joints, organs, or
the central nervous system. It can even cause death.
Description of Symptoms and Diagnoses
From the date of exposure to the onset of symptoms is the incubation period. The CDC (2014) claims
that the symptoms can occur between “3 -15 weeks after being exposed.” The symptoms that can occur
after exposure to Blastomyces dermatitidis vary greatly. Symptoms to different body parts include:
cutaneous, bone, central nervous system, and other sites of infection. According to the CDC (2014), only
50% of the people exposed will actually have symptoms. Some symptoms are very similar to flu like
symptoms; including fever, chills, cough, muscle aches, joint pain, chest pain, weight loss, and fatigue.
Most people diagnosed with blastomycosis also have skin symptoms, such as, pustules. Pustules are
small grayish bumps resembling warts on the skin that fill with fluid or pus. The pustules are typically
painless, although they can eventually lead to scarring of the skin. In serious cases the fungus can
spread to the “long bones, vertebrata, ribs, and the cranium in the form of osteomyelitis with
dissemination to the joints, where it may cause septic arthritis.” In the central nervous system, “patients
may manifest signs of meningitis, cerebral abscess, or granuloma formation associated with the
presence of Blastomyces dermatitidis.” Other body parts that can exhibit symptoms are the “breasts,
eyes, ears, thyroid, adrenal glands, myocardium, pericardium, or digestive tract (Lopez-Martinez,
Mendez-Tover 2012).”
Description of Treatment
Depending on the severity of the symptoms and diagnosis, medicine may or may not be needed.
According to Lopez-Martinez and Mendez-Tovar, “treatment should be prescribed without exception to
all patients with pulmonary blastomycosis, systemic dissemination to any organ, and
immunosuppression (2012).” Triazole drugs are prescribed for patients with mild pulmonary symptoms
with a “cure rate of 90%-95%” after 2-6 months of use. Other mild forms can just be monitored by the
patients’ physician. In patients who have severe pulmonary blastomycosis, amphotericin B is
prescribed. After the patient finishes the amphotericin B, they must follow that up that up with several
months of the triazole drugs. “Immunosuppressed patients are advised not to travel to endemic zones
and to avoid contact with dogs in these regions, due to reports of transmission of disease through dog
bites (Lopez-Martinez, Mendez-Tovar 2012).”
Description of Environment
According to Dworkin, Duckro, Proia, Semel, and Huhn, (2005) Blastomyces dermatitidis can be found
throughout the world, but is most common in parts of North, Central and South America. In the United
States it is typically found in the Southeast and Midwest. More specifically, the fungus is found in
regions surrounding the Mississippi River, the Great Lakes area, and the Ohio River. There have also
been outbreaks in Wisconsin, Illinois, New York, Louisiana and Colorado. The fungus has also been
reported worldwide; Canada, Africa, England, and India. Even though the fungus is primarily found in
rural locations there have been endemic outbreaks in non-rural areas near yard waste collection and
composting facilities, especially where pine tree litter is present. “Environmental and meteorological
conditions and material management practices were identified that may have facilitated growth and
dispersal of B. dermatitidis conidia near this residential area (Phister, Archer 2010).”
Description of Susceptibility
People who live in endemic areas and engage in activities that expose them to woods or river banks are
at a higher risk. Studies have shown that occupationally, farmers and forestry workers are the most
common professions exposed. People who partake in rural activities such as hunting, fishing, gardening,
hiking, and camping are more susceptible than non-rural activities. According to CDC.gov (2014), anyone
can be exposed to Blastomyces dermatitidis but patients with underlying defects in T cell and other
personal health issues are more susceptible. According to cmr.asm.org (2014), “B. dermatitidis appears
no more likely to cause disease in a person with compromised cellular immunity than to cause disease in
a normal host. The presence of natural defenses against inhaled conidia in the lung may explain this
observation. When blastomycosis does occur in immunocompromised patients, the disease is more
aggressive than in immunocompetent hosts.” Outside of humans, canines are the most commonly
affected but other animals such as cats, tigers, lions may also develop the disease.
Description of Exposure
According to the CDC (2014), Blastomyces dermatitidis is found in soil and molds which enter the body
through inhalation of asexually produced spores into the respiratory tract. Other rare forms of
transmission included, inoculation, dog bites, conjugal transmission, and intrauterine transmission.
Conclusions Leading to a Hypothesis
Based upon my research of blastomycosis thus far, I have found that most case studies have specifically
focused upon only one aspect of descriptive epidemiology: geographical location of the exposure to
explain epidemiological outbreaks. I believe that this is because blastomycosis can only occur in certain
geographical locations throughout the world, and more specifically, in certain parts of the United States
and Canada. This is where I feel there is a gap in the research. I am going to use historical data and a
cross sectional study to research whether or not descriptive epidemiologic attributes contribute to
incidence of blastomycosis. The descriptive epidemiological variables researched are: age, gender, race,
location, and job specific incidents.
Null Hypothesis: There is no correlation between age, gender, and race in incidence of blastomycosis.
Predicted Outcome: The null hypothesis will be rejected. There will be a correlation between age,
gender, and race after comparing specific case.
There are many small outbreaks of blastomycosis throughout the United States, Mexico, and Canada. I
completed a cross-sectional study by researching specific case studies and analyzed these studies to find
any descriptive epidemiological patterns between the outbreaks. There were a total of 6 smaller
outbreaks with 17 individual patients that were diagnosed with blastomycosis used in the report and
one large outbreak in a county of Wisconsin from 1999-2005. In order to determine whether or not
descriptive epidemiological variables such as age, gender, race, and location, contribute to incidence to
blastomycosis, the specific case studies were compared to each other to determine any correlation
between the descriptive epidemiologic variables.
Brief Description of the case studies used:
1.
Expanding Epidemiology of Blastomycosis: Clinical Features and Investigation of 2 Cases in
Colorado
Colorado Outbreak: The first outbreak that was researched was a small outbreak in Colorado.
The two patients were coworkers working in the Front Range region of the Rocky Mountains.
They were engaged in a prairie dog relocation project and were exposed to contaminated soil.
The median age was 30. There were 2 males and 0 females during this outbreak. The race was
not specified.
Location
Median Age
Gender
Male
Female
Race
Occupation
Colorado
30
2 (100%)
0 (0%)
N/A
Prairie Dog Relocation
2. Blastomycosis
Tennessee Outbreak: This outbreak was a single case where the patient was a tire plant
employee. The patient was a 28 year old male and his race was unidentified.
Location
Median Age
Gender
Male
Female
Race
Occupation
Tennessee
28
1 (100%)
0 (0%)
N/A
Tire Plant Worker
3. Blastomycosis imported to Monterrey, Mexico: fifth case reported in Mexico
Mexico Outbreak: The outbreak consisted of 5 patients. Although, they traveled to and were
diagnosed in Mexico, the patients were all originally from the United States. One of the patients
was an over the road truck driver, the other 4 patients occupations was not disclosed. There
were 5 males and 0 females diagnosed with blastomycosis. There was no race information and
the median age was 38.8
Location
Mexico
Median Age
Gender
Male
Female
Race
Occupation
38.8
5 (100%)
0 (0%)
N/A
N/A
4. The Epidemiology of Blastomycosis in Illinois and Factors Associated with Death
Illinois Outbreak: A case study from Illinois tracked 500 cases of blastomycosis from January
1993 to August 2002. Of the 500 cases they selected 4 case studies. The median age was 36.25,
there were 2 males and 2 unknown genders, and there were no races listed.
Location
Median Age
Gender
Male
Female
Unknown
Race
Illinois
36.25
2 (50%)
0
2 (50%)
N/A
5. Pulmonary Blastomycosis: a New Endemic Area in New York State
New York Outbreak: According to the research there have only been 3 people exposed to
blastomycosis in the state of New York. Two of the cases occurred in 2012, and one occurred in
2007. The two cases that occurred in 2012 were in the same county. The median age of the
outbreak was 42 years old. There were 3 males and 0 females, which mean 100% of the
patients were males. The race of the patients was not listed.
Location
Median Age
Gender
Male
Female
Race
New York
42
3 (100%)
0 (0%)
N/A
6. Using Local Epidemiology to Make a Difficult Diagnosis: a Case of Blastomycosis
Ontario Outbreak: This case study used one patient. This patient was a seasonal worker. He
had recently quit working on a construction project clearing brush and digging ditches in
Northwestern Ontario. The median age was 21, there was 1 male and 0 females, and no races
listed.
Location
Median Age
Gender
Male
Female
Race
Occupation
Winnipeg
21
1 (100%)
0 (0%)
N/A
Excavator/Construction
7. Blastomycosis-Wisconsin 1986-1995
Wisconsin Outbreak: Wisconsin has one of the highest rates of blastomycosis and is also a state
that is required to report blastmycosis cases. During this time 636 cases of blastomycosis were
reported to the DOH statewide. The median age is 46 years old for the cases in Wisconsin.
There were 381 males and 254 females diagnosed with blastomycosis, which is 60% and 40%
respectively. There was no data related to race of any of the outbreaks and occupations were
Location
Median Age
Gender
Male
Female
Race
Occupation
Wisconsin
46
381 (60%)
254 (40%)
N/A
Excavator/Construction
Descriptive Epidemiological Patterns
Race: In all of the case studies the race of the patients was not discussed in any of the studies. There
have been no links between race and blastomycosis.
Age: There were a wide variety of ages for the patients with blastomycosis throughout all of the case
studies. The ages in all cases were very random. The ages ranged from 4 months – 95 years. The
median age for all of the case studies was 40.9 years old.
Gender: There were 395 males, 254 females, and 2 unknown genders in all cases. This is a large trend
that shows more males are diagnosed with blastomycosis than females.
Location: Each of the case studies took place in different locations. The locations were from Colorado,
Mexico, Illinois, New York, Ontario, Tennessee, and Wisconsin. The case study in Colorado took place in
the Front Range region of the Rocky Mountains. The Mexico outbreak states that the patients were
traveling to endemic areas and that there was no confirmation of the exposure in Mexico. The case
study in Ontario took place in Northwestern Ontario. He was a seasonal worker dealing with excavation.
Of the 3 case studies in New York, 2 of the cases occurred in Otsego County and 1 occurred in Herkimer
County. Both counties are not along the St. Lawrence River. The St. Lawrence River was an endemic
area reported in dogs. None of the patients traveled from their resident counties.
Overall Data
Case Study Outbreaks
(n=651) n(%)
Gender
Male
Female
Unknown
Median Age
Race
395 (60%)
254 (39%)
2 (.003%)
40.9 Years
Not Known
Conclusion
Based on the above data, men aged 40 years old, of any race have a higher incidence rate to
blastomycosis. 60% of males in the case studies were more likely to get blastomycosis than females.
The median age for all case studies was 40.9 years of age. There was a very wide range of patients that
were diagnosed with blastomycosis; from 4 months to 95 years of age. A correlation between race and
blastomycosis was not found because there was insufficient information provided to make any
comparisons. Most common incidences occurred in rural, wooded, and riverbed areas.
In my opinion there are many reasons for this outcome. Men are more likely to work in endemic areas
outside performing construction, excavation etc. than women. Men may also be more likely to have
outdoor hobbies such as fishing, hunting, hiking, etc. Some of the outbreaks occurred due to the job
duties of the patients. The job professions included Tanner, Excavation, Laborer, Prairie Dog Relocation,
Truck Driver, and a Tire Plant Worker. The seasonal laborer and the 2 prairie dog relocaters worked
directly with soil and brush. Since blastomycosis occurs mainly in people that work or have outdoor
hobbies the occupations listed were not surprising.
The original null hypothesis stated that there was no correlation between age, gender, race, and
location in incidence of blastomycosis. The predicted outcome was that the null hypothesis would be
rejected, and there would be a correlation between age, gender, race, and location after comparing
statistical data. The null hypothesis was not entirely proven or disproven. There was a correlation
between age and gender and blastomycosis. There was no correlation between race and blastomycosis.
The rural, wooded, and riverbed areas did contribute to some incidence of blastomycosis but did not
hold true for all cases.
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