ARCHIVED - Locally Acquired Histoplasmosis Cluster, Alberta, 2003
Histoplasmosis is an endemic mycosis; its prevalence in Canada is thought to be limited to central Canada, with no reported infections acquired in the western provinces. We report the occurrence of Histoplasma capsulatum infection in a woman with no travel history or exposure history outside of Alberta within the incubation period, and the subsequent identification of a cluster of acute infections among coworkers.
Case report and cluster investigation
A 25-year-old, healthy woman presented to her family physician with a 5-day history of headache, myalgias, nausea, vomiting, and fever. She had developed a dry cough, pleuritic-type chest pain, and mild dyspnea, and was referred to the hospital. Chest radiography was reported as showing a diffuse nodular pattern. A careful review of the patient's occupational, travel, and other exposure history was undertaken. She normally resided in a village in Newoundland but had relocated to Alberta 5 months before the illness began. There was no other travel history. She was not aware of tuberculosis exposure and had no risk factors for HIV infection.
On admission, physical examination and initial laboratory investigations were normal. Thoracic computed tomography revealed numerous small, well-circumscribed, soft tissue nodules spread randomly and diffusely throughout both lungs. Sputum culture was nondiagnostic, and serologic tests were initially negative for histoplasmosis, HIV, Mycoplasma pneumoniae, blastomycosis, chlamydia, tularemia, coxiella, and legionella.
Video-assisted thorascopic lung biopsy yielded necrotizing granulomata that were bronchiolocentric. These were felt to be consistent with an infectious etiology, although stains did not reveal an organism. Given the suspicion of an inhaled agent, serologic tests for fungi were repeated. This time, histoplasmosis serology demonstrated both H and M bands by immunodiffusion (ID). In the ensuing period, cultures of the lung biopsy material yielded H. capsulatum, and itraconazole therapy was initiated.
The patient's employment immediately preceding presentation to hospital was as a maintenance worker at a golf course near Edmonton. She reported that coworkers had experienced similar symptoms at approximately the same time as her own in the days following the renovation of a fairway on the golf course (sod and tree removal, grading and sod replacement) during late September and early October.
Clinical and exposure information was collected from a core group of seven people who worked alongside the index case at the golf course. Serologic testing was performed, which identified a further three cases.
An 18-year-old male member of the golf course grounds maintenance crew who worked on the renovation project developed fever, chills, headache, myalgias, chest pain with deep inspiration, anorexia, and fatigue during the same period as the index case. He did not seek medical attention. Four weeks after illness onset the ID test for H. capaslatum was positive for H and M bands. Chest radiography demonstrated no abnormalities.
A 21-year-old male member of the grounds maintenance crew who worked on the renovation project noted fatigue that began on the same day as that of Case A. Fever, chills, nausea, headache, and myalgias developed over the next week, gradually resolving over 2 weeks. ID was reported as negative, although there was one line of nonidentity observed. A second sample was drawn 6 weeks after the illness began and was positive by ID for H. capsulatum H and M bands. It was also referred to the Centers for Disease Control and Prevention (CDC), Atlanta, for complement fixation analysis (CF) and ID. Both assays were positive, the ID exhibiting both H and M bands and the CF having a titre of 1:8 for histoplasmin and ≥ 1:256 for whole yeast.
A 37-year-old male grounds crew supervisor worked on all aspects of grounds maintenance, including the renovation of the fairway. He was generally well and had had no illness during the period of interest. Serological testing was undertaken. As in case B, one line of nonidentity was seen. A second sample was drawn 2 weeks later (6 weeks after the start of illness in the index case) and referred to the CDC. ID for H. capsulatum was reported as positive for M band only, and the CF assay for histoplasmin and whole yeast were reported as positive with titres of 1:4 and 1:64 respectively.
Environmental exposures at the golf course were investigated as a possible source of the illness cluster. No bird or bat roosting sites were found on the golf course during a site inspection. Replacement sod had been acquired from British Columbia.
Caused by the dimorphic fungus H. capsulatum, histoplasmosis is endemic in parts of the United States, South America, Southeast Asia, Africa, and Australia. Specifically, the largest endemic areas are the Ohio and Mississippi River valleys, the Amazon River valley, and the Mekong River valley. Its occurrence in Canada is thought to be limited to central Canada, along the Saint Lawrence River(1). There have been no reported infection clusters acquired in the western provinces.
Soil that favours growth of this mould is often moist, acidic, and contaminated by bird or bat droppings, which provide nutrients for sporulation(2). Symptoms of histoplasmosis typically develop between 7 and 14 days after exposure to spores. As inhalation is the near universal route of acquisition of this agent, environmental risk factors usually involve the disruption of soil or other inoculated material. Aerosols can be generated through excavation projects, construction or demolition, cleaning of sites with accumulated bird or bat droppings, and cave treks(3-5). Exposure to disturbed soil clearly occurred during the incubation period for cases in the series presented, demonstrating the development of histoplasmosis in a cluster.
We report the first known locally acquired point source cluster of histoplasmosis in western Canada. Although the infection is not uncommon in many regions of the United States and Ontario, where similar point source clusters occasionally occur, the prevalence of this pathogen outside of these areas is not well known. Underdiagnosis may occur in Alberta because of perceived lack of endemicity. This cluster illustrates histoplasmosis infection in individuals with no travel outside of Alberta during the incubation period, suggesting the existence of at least a local microfocus of H. capsulatum. A clinical suspicion for this infection should be maintained in those patients presenting with compatible symptoms following high-risk activities in Alberta, as its presence in the region has now been demonstrated.While histoplasmosis is not currently notifiable(6), Alberta's provincial health authority is considering adding it to the schedule of individually notifiable diseases in provincial public health legislation to facilitate surveillance.
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Government of Alberta. Public Health Act Communicable Diseases Regulation 238/85. Edmonton: Queen's Printer, 2001.
Source: H Anderson, MD, G Taylor MD, EA Fanning, MD, Department of Medicine, University of Alberta; L Honish, MSc, M Johnson, MD, J Jaipaul, BScN, S Probert, MSc, C Tovstiuk, BScN, Public Health Division, Capital Health; G Tyrrell, PhD, Provincial Laboratory of Public Health; R Rennie, PhD, C Sand, BSc, National Centre for Mycology, Edmonton, Alberta.
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