Blastomycosis final revison

Patterns in Descriptive Epidemiological Variables in Blastomycosis Outbreaks

By: Bill Luebke

Epidemiology

Abstract

Background:  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.

Method:  I will conduct a cross-sectional study by researching specific case studies and analyze these studies to find any descriptive epidemiological patterns between the outbreaks: age, race, and gender.  Objective:  Previous case studies have been conducted, but are limited to specific outbreaks in a region.   The objective is to use the specific case studies per region to find correlations between age, race, and gender.

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.”  In other words,  blastomycosis developes when a spore produces asexually and is suspended in the air in the form of microscopic particles.  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 (inflammation) with dissemination (spreading) 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 (spreading) 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 other sources (cmr.asm.org) (2014), Blastomyces dermatidis is no more likely to cause disease in a person with a compromised immune system than a perfectly healthy person.    When blastomycosis does occur in patients that have a compromised immune system, the disease is more aggressive than in a perfectly healthy person.

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, and race.

Null Hypothesis:  There are no other variables besides geographical location that cause blastomycosis.

Alternative Hypothesis:  There are other variables besides geographical location that cause blastomycosis.

Predicted Outcome:   The null hypothesis will be rejected.  There will be other epidemiological variables such as age, gender, or race that contribute to causing blastomycosis, instead of just geographical location.

Research and Methods

There are many small outbreaks of blastomycosis throughout the United States, Mexico, and Canada.  In my research I found that each specific case study looked at and analyzed the epidemiological patterns such as age, race, and gender, within its specific geographical location.  I will complete a cross-sectional study.  A cross-sectional study “examines the relationship between diseases (or other health related characteristics) and other variables of interest as they exist in a defined population at one particular time.”  I will use historical data to research specific case studies and analyze these studies to see if there are any epidemiological patterns such as age, race, or gender between the outbreaks.  Compiling the data from each specific case study will help me prove or disprove my hypothesis.

I gathered historical data from 6 smaller outbreaks with 17 individual patients that were diagnosed with blastomycosis from North American 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, and race contribute to incidence to blastomycosis, the specific case studies were compared to each other to determine any correlation between the descriptive epidemiologic variables.

Historical Data – Brief Description of the case studies used: 

  1. 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

Colorado

Median Age

30

Gender

  Male

2 (100%)

  Female

0 (0%)

Race

N/A

Occupation

Prairie Dog Relocation

 

  1. 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

Tennessee

Median Age

28

Gender

  Male

1 (100%)

  Female

0 (0%)

Race

N/A

Occupation

Tire Plant Worker

 

  1. 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

38.8

Gender

  Male

5 (100%)

  Female

0 (0%)

Race

N/A

Occupation

N/A

 

  1. 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

Illinois

Median Age

36.25

Gender

  Male

2 (50%)

  Female

0

  Unknown

2 (50%)

Race

N/A

 

  1. 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

New York

Median Age

42

Gender

  Male

3 (100%)

  Female

0 (0%)

Race

N/A

 

  1. 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

Winnipeg

Median Age

21

Gender

  Male

1 (100%)

  Female

0 (0%)

Race

N/A

Occupation

Excavator/Construction

 

  1. 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

Wisconsin

Median Age

46

Gender

  Male

381 (60%)

  Female

254 (40%)

Race

N/A

Occupation

Excavator/Construction

 

Conclusion

If a researcher analyzed the data in the case studies above, I believe they would find a correlation with age, gender, and race that attributes to the cause of blastomycosis.  With this prediction the alternative hypothesis would be accepted and the null hypothesis would be rejected.

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