The Dangers of Gardening: Sporotrichosis
ABSTRACT & COMMENTARY
Synopsis: An outbreak of lymphocutaneous sporotrichosis occurred in a group of tree nursery workers exposed to sphagnum moss.
Source: Hajjeh R, et al. Outbreak of sporotrichosis among tree nursery workers. J Infect Dis 1997;176:499-504.
Hajjeh and colleagues report their investigation of an outbreak of lymphocutaneous sporotrichosis among workers at a tree nursery in Florida. The attack rate was 14%, with nine of 65 employees having clinically evident disease. All those affected had been involved in the production of topiaries (plants shaped into ornamental forms). This activity involved "covering metal frames with chicken wire, filling the forms with sphagnum moss, and planting small ivy plants into the sphagnum moss."
Multivariate analysis found that working with sphagnum moss and filling topiaries, as well as having less prior gardening experience, were associated with increased risk of infection, while wearing gloves appeared protective.
Sporothrix schenkii was isolated from lesions of five patients and from four of 13 samples of sphagnum moss. Restriction fragment length polymorphism analysis of DNA extracted from these isolates found that, while the five patient isolates appeared identical with each other, they differed somewhat from the environmental isolates.
Eight of nine patients were initially treated with saturated solution of potassium iodide (SSKI); therapy in two of these was changed to itraconazole while one received this latter drug from the start.
COMMENT BY STAN DERESINSKI, MD, FACP
S. schenkii is a thermal dimorph that grows in vitro as a yeast at 37°C and in hyphal form at lower temperatures. It is resistant to cycloheximide in fungal culture media and grows well at 25-30°C but poorly or not at all at temperatures greater than 35°C. Off-white to cream-colored colonies with wrinkled surfaces appear after a few days of incubation but eventually develop brown to black pigment. The fungus is found in decaying plant matter and has a worldwide distribution.
Cases of sporotrichosis have previously been traced to exposure to sphagnum moss. An outbreak of sporotrichosis in 1988 involving 84 cases in 15 states was also traced to sphagnum moss that had come, as the moss in the instance reviewed here, from Wisconsin.1 Infection usually occurs, as undoubtedly occurred in the cases reviewed here, by direct inoculation with consequent development of the lymphocutaneous form of the disease. This form is characterized by a nodule at the site of inoculation that subsequently ulcerates in association with a string of nodular lesions along the lymphatic drainage. While highly suggestive of sporotrichosis in the context of an appropriate epidemiological history, a variety of other organisms, including Nocardia, mycobacteria (especially, M. marinum), Leishmania, and Francisella may cause similar findings.2 Less often, inhalation of conidia may occur, with consequent pulmonary infection. Dissemination may rarely occur to any body site.
Lymphocutaneous sporotrichosis may respond to orally administered SSKI, an agent whose mechanism of action remains unknown.3 SSKI is, however, often poorly tolerated, at least in adults, and, furthermore, is ineffective in other, more invasive forms of the disease.4 Lymphocutaneous sporotrichosis has been treated with the application of heat, taking advantage of the inability of many strains to survive at elevated temperatures.5 Sporotrichosis may be treated with amphotericin B, which has been largely reserved for systemic, deep infections. More recently, itraconazole has been demonstrated to be effective in treatment of deep as well as lymphocutaneous infection.6,7 Fluconazole is less effective.8 Terbinafine was effective in all five patients with the lymphocutaneous form to whom this drug was administered in one series.9
References
1. Dixon DM, et al. J Clin Microbiol 1991;29:1106-1113.
2. Kostman JR, DiNubile, MJ. Ann Intern Med 1993;118:883-888.
3. Rex JH, Bennett JE. J Med Vet Mycol 1990;28:185-189.
4. Cabezas C, et al. Pediatr Infect Dis J 1996;15:352-354.
5. Hiruma M, et al. Mycoses 1992;35:11-12,293-299.
6. Sharkey-Mathis PK, et al. Am J Med 1993;95:279-285.
7. Kauffman CA. Clin Infect Dis 1995;21:981-985.
8. Kauffman CA, et al. Clin Infect Dis 1996;22:46-50.
9. Hull PR, Vismer HF. Br J Dermatol 1992;126 (S139): 51-55.
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