After the detection of Legionella in the BWTP effluent, a sludge filter defect was identified and repaired.
The sequence type ST1646, found in 5 patient isolates and in the environmental samples, identified the BWTP as the most likely source for both LD clusters.
The transmission models outcome, which posited a single hotspot near the BWTP, offers further support for the BWTP as the putative source of infection.
BWTP, biologic wastewater treatment plant; ST, sequence type.
BWTPs have been identified as the source of previous LD outbreaks (6-10).
Documented outbreaks associated with BWTPs have involved an additional disseminator, such as a WCT or river, in the dissemination of contaminated aerosols, usually marked by a sudden increase in cases.
Transmission from WCTs has been described as occurring at a distance of up to 12 km (11), whereas direct aerosol dispersal from BWTPs has been detected at a distance of up to 300 m (8).
Because our results indicate direct dispersal over a large distance of >1.6 km, further investigations should consider nontraditional Legionella sources, like BWTPs, as possible sources for sporadic LD cases.
Even though Cucamonga Creek water has a highly variable turbidity, the BWTP demonstrates positive performance.
The successful operation of the BWTP and other similar micro filtration plants will lead to increased regulatory acceptance and greater use of the technology.
Thanks to the BWTP, not only does the district meet current and projected community water needs, but the membrane facility will provide an affordable and efficient system for decades to come.