The health department says a large pile of pine needles at Merrill's yard waste site is the likely source of a rare fungal infection that led to the death of a 16-year-old girl and sickened 20 others last year.

State Epidemiologist John Archer says weather patterns and soil conditions contributed to the outbreak of blastomycosis. He says it was likely the largest urban outbreak in the country.

Tristan Muenchow, a Merrill High School junior, died February 14th of last year from the fungal infection. She lived next door to the waste site.

Thirteen of the people who got sick lived within a half-mile of the yard waste site and three others had almost daily exposure to it.

State Microbiologist John Pfister says 9 months of drought in early 2005 followed by rain in the fall might have created an environment for the fungus to grow in the pile of pine needles and release spores.