Volume 24, Number 10—October 2018
    
    Dispatch
Two Community Clusters of Legionnaires’ Disease Directly Linked to a Biologic Wastewater Treatment Plant, the Netherlands
Table 2
Results of environmental samples taken during investigation of 2 community clusters of Legionnaires’ disease directly linked to a biologic wastewater treatment plant, Boxtel, the Netherlands, October 2016–December 2017*
| Location of samples | Sampling date, wk/y | CFU/L | Legionella pneumophila serogroup | ST | 
|---|---|---|---|---|
| Water samples† | ||||
| BWTP | ||||
| Pond 1 (low aeration) | 48/2017 | 2.0 × 106 | sg1 | ‡ | 
| 50/2017 | 5.6 × 107 | sg1 | ST1646 | |
| Pond 2 (no aeration) | 48/2017 | 7.1 × 108 | sg1 | ST1646 | 
| 50/2017 | 19.2 × 108 | sg1 | ST1646 | |
| Pond 3 (high aeration) | 48/2017 | 15.0 × 108 | sg1 | ST1646 | 
| 50/2017 | 22.6 × 108 | sg1 | ‡ | |
| Municipal waste water treatment plant | ||||
| Influent | 39/2017 | 1.0 × 105 | sg1 | ST1646 | 
| Pond | 39/2017 | 2 × 103 | sg1 | ST1646 | 
| River midstream | 39/2017 | 2 × 103 | sg1 | ST1646 | 
| Riverside | 39/2017 | 2 × 104 | sg1 | ST1646 | 
| Fountain, city center | 50/2016 | Negative | ||
| 39/2017 | Negative | |||
| WCTs and air scrubbers next to BWTP, industrial area | ||||
| 50/2016 | Negative | |||
| 39/2017 | Negative | |||
| 48/2017 | Negative | |||
| 4 WCTs, industrial area | 50/2016 | Negative | ||
| 5 WCTs, industrial area | 39/2017 | Negative | ||
| Misting device, industrial area | 39/2017 | Negative | ||
| Other environmental samples† | ||||
| Biologic waste water treatment plant | ||||
| Air sample inside pond 3 tent | 50/2017 | Positive | sg1 | ‡ | 
| Swab inner surface pond 3 tent | 50/2017 | Positive | sg1 | ST1646 | 
*Source: Database National Reference Laboratory for Legionella, Haarlem, the Netherlands. BWTP, biologic wastewater treatment plant; sg, serogroup; ST, sequence type; WCT, wet cooling tower.
†Water samples were analyzed with an accredited in-house developed method based on ISO 11731:2017, with an additional step of acid treatment. Air samples were collected using a SASS 2300 air sampler (Research International, Seattle, WA, USA), and analyzed in with an accredited in-house developed method based on ISO 11731:2017.
‡Sequence type profile was incomplete because of technical problems experienced during mompS typing; however, for all 6 available alleles, results were in accordance with the ST1646 profile (flaA, 2; pile, 10; asd, 14; Mip, 10; mompS, not available; proA, 4; neuA, 11).
