BACKGROUND: Legionnaires’ disease is the second most common form of bacterial pneumonia in the United States. Nationally, the reported incidence has increased by 286% from 2000 to 2014. The age-adjusted incidence of legionellosis, which includes Legionnaires’ disease, in Allegheny County, Pennsylvania, is about four times higher than the US age-adjusted rate. Reasons for this elevated incidence are unknown. Cooling towers have been linked to outbreak related and non-outbreak related legionellosis. Proper cooling tower maintenance and disinfection are imperative for legionellosis prevention but not monitored in Allegheny County. To investigate cooling tower maintenance, disinfection practices, and Legionella positivity in Allegheny County, the Allegheny County Health Department (ACHD) performed a survey of building managers and tested cooling towers for Legionella pneumophila (LP).
METHODS: Building managers of facilities that house susceptible populations (hospitals, nursing homes, senior apartment buildings) and of city and county owned buildings were interviewed about the existence of a cooling tower, relevant maintenance practices, and permission to test for Legionella. At consenting facilities, ACHD sampled and cultured 100 mL of cooling tower basin water for LP. T-tests along with stepwise multivariable linear regression were used to assess associations between cooling tower characteristics and maintenance practices and the continuous outcome of LP positivity (colony forming units (CFU)/mL).
RESULTS: Of 408 building managers contacted, 377 (92%) completed the survey. Of these, 56 (15%) had a cooling tower (including 78% of hospitals, 10% of nursing homes, 17% of senior apartment buildings, and 6% of city/county owned buildings); 42 (75%) consented to testing. Of 42 cooling towers sampled, 20 (48%) tested positive for LP (median = 35 CFU/mL; range 10 – 2,000 CFU/mL). Factors associated (p < 0.05) with LP included older age, year round usage, lack of regular basin emptying, multiple cooling towers onsite, hospital as the facility type, and receiving municipal water treated at a secondary treatment plant. Significant variables in the multivariable analysis were older age (Coefficient: -21.1, CI: -33.7, -8.5) and regular basin emptying (Coefficient: -280.7, CI: -479.9, -81.4).
CONCLUSIONS: Given this survey found relatively low LP levels and ongoing maintenance on most cooling towers, ACHD does not recommend formal regulation of cooling towers at this time. Cooling tower owners are encouraged to develop a risk assessment plan in compliance with ASHRAE Standard 188, empty basin water annually, test basin water for Legionella at least annually, and increase frequency of inspections.