Human Blastomycosis Surveillance in
Minnesota,1999-2010
Carrie Klumb1,2, Kirk Smith1, Joni Scheftel1
1Minnesota
Department of Health
2CSTE/CDC Applied Epidemiology Fellowship
Background
• Blastomycosis is caused by the dimorphic
fungus Blastomyces dermatitidis
• Growth dependent on weather and
environmental factors (e.g., recent rainfall,
soil acidity)
– Fastidious organism
– Extremely difficult to isolate from the
environment
Background (cont.)
• Infection occurs through inhalation of airborne
spores from disturbed soil
• Approximately 50% of infections asymptomatic
or resolve spontaneously
Background (cont.)
• Median incubation period is 45 (range, 21 to
106 days)
• Acute infections present with sudden fever,
cough, and pulmonary symptoms of varying
severity
• National case fatality rate is approximately
5%
Blastomycosis Endemic Regions of
North America (in brown)
Fang et al. Radiographics 2007;27:641-655.
Study Objective
Review surveillance data from 1999 to 2010
to better describe the burden and
epidemiology of blastomycosis in
Minnesota
Methods
• Human blastomycosis cases are reportable in
Minnesota
• Passive surveillance using standard report
form
• Each case interviewed by MDH staff
regarding health history, symptoms, and
potential exposures during 3 months prior to
onset
– Likely county of exposure determined
from interview
Methods - Case Definition
• A Minnesota resident with either:
a) B. dermititidis cultured or visualized
from tissue or bodily fluids
OR
b) A positive urine antigen test for B.
dermititidis and compatible clinical
symptoms
• Case inclusion criteria: cases with a
diagnosis date between January 1, 1999 and
December 31, 2010
Methods (cont.)
• Fatal blastomycosis cases compared to
hospitalized non-fatal cases to examine
possibility of delayed diagnosis
• Descriptive analyses were performed using
SAS, version 9.2
• ArcMap version 9.3.1 used to identify highly
endemic counties in Minnesota
Results
• 389 cases of blastomycosis diagnosed and
reported to MDH from 1999 to 2010
– Incidence: 0.58 cases/100,000 person-yrs
• 371 (95%) cases sporadic
– 71% (n=265) male
– Median age: 44 yrs (range, 3 to 93 yrs)
– 31% (90/289) underlying conditions
– 67% (n=247) hospitalized
– 11% (n=39) fatal
Demographic Characteristics of Human
Blastomycosis Cases, Minnesota, 1999-2010
(n=371)
Age Group (yrs)
0-9
10-19
20-29
30-39
40-49
50-59
60-69
≥70
No. (%)
5 ( 1)
42 (11)
44 (12)
66 (18)
73 (20)
68 (18)
26 ( 7)
43 (12)
56%
Demographic Characteristics of Human
Blastomycosis Cases, Minnesota, 1999-2010
Race (n=305)
No. (%)
White
American Indian
Black
Asian
Other
256 (84)
23 ( 8)
12 ( 4)
12 ( 4)
2 (0.7)
Ethnicity (n=201)
No. (%)
Non-Hispanic
Hispanic
190 (95)
11 ( 6)
% MN
Population
85
1
5
4
2
% MN
Population
95
5
Symptoms Reported by Cases,
Minnesota, 1999-2010 (n=371)
Symptom
Cough
Fatigue
Fever
Weight Loss
Night Sweats
Chest Pain
Headache
Skin Sores
Cough with Blood
No. (%)
258 (70)
229 (62)
210 (57)
175 (47)
161 (43)
157 (42)
113 (30)
91 (25)
68 (18)
Clinical Characteristics of Human
Blastomycosis Cases, Minnesota, 1999-2010
Characteristic
Disease Location
Pulmonary
Disseminated
Extra-pulmonary*
No. (%)
n=339
229 (68)
81 (24)
29 ( 9)
*Typically a soft tissue infection following a wound
Clinical Characteristics of Human
Blastomycosis Cases, Minnesota, 1999-2010
Characteristic
No. (%)
Diagnosis Method
n=371
Culture
Smear
Histopathology
Urine Antigen
304 (82)
142 (38)
54 (18)
19 ( 5)
Clinical Characteristics of Human
Blastomycosis Cases, Minnesota, 1999-2010
Treatment Type
Antifungals
Itraconazole
Amphotericin B
Fluconazole
Voriconazole
Other Antifungals
Antibiotics Only
Surgical Removal
n=314
221 (79)
51 (18)
11 ( 4)
5 ( 2)
7 ( 5)
14 ( 5)
2 ( 1)
Hospitalized Cases
No. Underlying
Conditions
(%)
Days
hospitalized,
median (range)
Days admission
to testing,
median (range)
Fatal
Cases
n=39
Non-fatal
Cases
n=205
p-value
15 (38)
52 (25)
0.09
9
(3 to 48)
7
(1 to 137)
0.03
4
(0 to 32)
1
(0 to 60)
0.02
Number of Blastomycosis Cases in
Minnesota by Year of Diagnosis,
1999-2010 (n=371)
40
No. of Cases
35
30
25
36
31
33
33
30
28
33
35
36
28
25
23
20
15
10
5
0
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
Year of Diagnosis
Human Blastomycosis Cases by Month of
Onset, Minnesota, 1999-2010 (n=324)
45
39
No. of Cases
40
34
32
35
30
25
20
28
27
20
38
20
18
24
25
19
15
10
5
0
Jan Feb Mar Apr May Jun
Jul Aug Sep Oct Nov Dec
Month of Onset
Human Blastomycosis cases by Season of
Onset, Minnesota, 1999-2010 (n=324)
120
105
No. of Cases
100
77
80
77
65
60
40
20
0
Spring
Mar-May
Summer
Jun-Aug
Fall
Sept-Nov
Season of Onset
Winter
Dec-Feb
Results (cont.)
• 237 (64%) cases had probable county of
exposure in Minnesota
– 176 (74%) of those cases exposed in
county of residence
• 33 (9%) cases likely exposed outside of
Minnesota
• 101 (27%) cases had unknown county of
exposure
Human Blastomycosis Cases by Probable
County of Exposure, 1999-2010 (n=237)
Beltrami
Itasca
St.
Louis
Number of Cases
Cass
0
1
2-7
Chisago
Washington
8-12
13-29
30-69
Human Blastomycosis Incidence,1999-2010
Cases that were Exposed in County of
Lake of the
Residence (n=176)
Woods
Cook
Itasca
Incidence per 100,000
person-years
Big
Stone
0
0.10-0.58
0.59-1.10
1.20-2.50
2.60-4.62
Minnesota Biomes
Tallgrass
Aspen
Parkland
Coniferous
and Mixed
Forest
Minneapolis-St. Paul
Metropolitan Area
Prairie
Deciduous
Grassland Forest
Modified from Minnesota DNR, http://www.dnr.state.mn.us/biomes/index.html
Exposure Frequency Among Cases
(n = 273*)
Exposure/Activity
Woodcutting
Gardening
Fishing
Excavation
Hiking
Cabin
Hunting
Camping
%
38
31
31
30
27
26
19
15
*Median number of cases with one or more exposures
Discussion
• Statewide incidence of 0.58 cases per 100,000
person-years
– Ranges from 0 to 4.6 cases per 100,000
person-years
• Northeast and North central part of the state
most endemic
– Coniferous and Mixed Forest Biome
• Recently more cases along St. Croix River
bordering Wisconsin
Minnesota Biomes
Tallgrass
Aspen
Parkland
Coniferous
and Mixed
Forest
Chisago and
Washington Counties
Prairie
Deciduous
Grassland Forest
Modified from Minnesota DNR, http://www.dnr.state.mn.us/biomes/index.html
Discussion
• Majority of cases are male and between 30
and 59 years of age
– Possibly due to gender-specific activities
• American Indians affected by blastomycosis
more than other minority groups. However,
higher populations in endemic region
• Case-control study necessary to better
answer these questions and determine
specific risk factors
– Recent IRB approval
Discussion
• Time from admission to diagnostic testing
significantly longer in fatal cases
– delayed diagnosis
• Data suggest early detection is critical in
preventing fatal outcome
Discussion
• Blastomycosis difficult to diagnosis
– Rare
– Symptoms begin as non-specific
respiratory illness
– Often confused with bacterial pneumonia
– Most common diagnosis method is culture
but takes 3 to 4 weeks
– Contributes to delay in diagnosis
Discussion
• Smears give same day results; Blastomyces
is pathognomonic
Conclusion
The association between delayed diagnosis and
case fatality indicate that increased awareness
among clinicians and the public could lead to
earlier detection and treatment, and reduced
mortality due to blastomycosis
Acknowledgments
Minnesota Department of Health
Brittani Schmidt
Linda Gabriel
Foodborne, Vectorborne, and Zoonotic Disease
Unit
Reporting Health Care Facilities