Human Blastomycosis Surveillance in Minnesota,1999-2010

Carrie Klumb1,2, Kirk Smith1, Joni Scheftel1

1Minnesota Department of Health2CSTE/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

• 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

Results

Demographic Characteristics of Human Blastomycosis Cases, Minnesota, 1999-2010

(n=371)

Age Group (yrs) No. (%)

0-9 5 ( 1)

10-19 42 (11)

20-29 44 (12)

30-39 66 (18)

40-49 73 (20)

50-59 68 (18)

60-69 26 ( 7)

≥70 43 (12)

56%

Demographic Characteristics of Human Blastomycosis Cases, Minnesota, 1999-2010

Race (n=305) No. (%)% MN

Population

White 256 (84) 85

American Indian 23 ( 8) 1

Black 12 ( 4) 5

Asian 12 ( 4) 4

Other 2 (0.7) 2

Ethnicity (n=201) No. (%)% MN

Population

Non-Hispanic 190 (95) 95

Hispanic 11 ( 6) 5

Symptoms Reported by Cases, Minnesota, 1999-2010 (n=371)

Symptom No. (%)

Cough 258 (70)

Fatigue 229 (62)

Fever 210 (57)

Weight Loss 175 (47)

Night Sweats 161 (43)

Chest Pain 157 (42)

Headache 113 (30)

Skin Sores 91 (25)

Cough with Blood 68 (18)

Clinical Characteristics of Human Blastomycosis Cases, Minnesota, 1999-2010

Characteristic No. (%)

Disease Location n=339

Pulmonary 229 (68)

Disseminated 81 (24)

Extra-pulmonary* 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 304 (82)

Smear 142 (38)

Histopathology 54 (18)

Urine Antigen 19 ( 5)

Clinical Characteristics of Human Blastomycosis Cases, Minnesota, 1999-2010

Treatment Type n=314

Antifungals

Itraconazole221 (79)

Amphotericin B51 (18)

Fluconazole11 ( 4)

Voriconazole5 ( 2)

Other Antifungals 7 ( 5)

Antibiotics Only14 ( 5)

Surgical Removal 2 ( 1)

Hospitalized Cases

Fatal Casesn=39

Non-fatal Casesn=205 p-value

No. UnderlyingConditions (%)

15 (38) 52 (25) 0.09

Days hospitalized,median (range)

9

(3 to 48)

7

(1 to 137)0.03

Days admission to testing, median (range)

4

(0 to 32)

1

(0 to 60)0.02

Number of Blastomycosis Cases in Minnesota by Year of Diagnosis,

1999-2010 (n=371)

3133

3028

36

2825

23

33 3335 36

0

5

10

15

20

25

30

35

40

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Year of Diagnosis

No

. of

Ca

ses

Human Blastomycosis Cases by Month of Onset, Minnesota, 1999-2010 (n=324)

20

32

18

27

19

34

24

39

28

38

25

20

0

5

10

15

20

25

30

35

40

45

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

No

. of

Ca

ses

Month of Onset

Human Blastomycosis cases by Season of Onset, Minnesota, 1999-2010 (n=324)

65

77

105

77

0

20

40

60

80

100

120

Spring Summer Fall Winter

No

. of

Ca

ses

Season of Onset

Mar-May Jun-Aug Sept-Nov Dec-Feb

• 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

Results (cont.)

Human Blastomycosis Cases by Probable County of Exposure, 1999-2010 (n=237)

Itasca

St. Louis

Chisago

Washington

Beltrami

CassNumber of Cases

0

1

2-7

8-12

13-29

30-69

Human Blastomycosis Incidence,1999-2010 Cases that were Exposed in County of

Residence (n=176)

Incidence per 100,000 person-years

0

0.10-0.58

0.59-1.10

1.20-2.50

2.60-4.62

Cook

Big Stone

Lake of the Woods

Itasca

Minnesota Biomes

                            

         

Coniferousand Mixed Forest

TallgrassAspen

Parkland

PrairieGrassland

DeciduousForest

Minneapolis-St. PaulMetropolitan Area

Modified from Minnesota DNR, http://www.dnr.state.mn.us/biomes/index.html

Exposure Frequency Among Cases(n = 273*)

Exposure/Activity %

Woodcutting 38

Gardening 31

Fishing 31

Excavation 30

Hiking 27

Cabin 26

Hunting 19

Camping 15

*Median number of cases with one or more exposures

• 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

Discussion

Minnesota Biomes

                            

         

Coniferousand Mixed Forest

TallgrassAspen

Parkland

PrairieGrassland

DeciduousForest

Chisago and Washington Counties

Modified from Minnesota DNR, http://www.dnr.state.mn.us/biomes/index.html

• 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

Discussion

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