A Legionnaires Disease outbreak occurred in Hong Kong between 1st – 29th February 2020 with seventeen (17) patients diagnosed with no fatality reported by CHP.
The total number of cases reported by CHP is lower than 17 reported here because additional cases residing physically close (<1000m) to the Choi Hung MTR station and the Ngau Chi Wan market were excluded without any evidence of the distinction. Ngau Chi Wan market is a very popular wet market in the area, located on Clearwater Bay road, directly above the Choi Hung MTR station, it is high traffic area, used by people from the local estates, and the surrounding districts.
In total 15 cases were declared by CHP, twelve (12) male, and three (3) female, most were elderly residing near Choi Hung / Ping Shek Estate in Hong Kong, most with underlying disease.
At least two Legionnaires disease cases (refer to the table below, cases 12 and 13) were not counted as part of this cluster, yet both people reside nearby, approx. 1000m from buildings with confirmed cases, and well within the typical range of infection caused by cooling towers.
CHP also reported on 4 March 2020, specimens from two (2) more patients, that is eight (8) in total, match the samples from two Choi Hung MTR station cooling towers taken before the towers were disinfected (by implication sampled before 4 Feb. 2020). What is unclear, the initial 6 patients were reported on 14-2-2020, and three weeks later the additional pair were reported.
The CHP report on 4 March 2020 [link] that the Choi Hung MTR cooling towers have been disinfected and the water sampling test result (not provided) was stated to be lower than the action level. However, the tower installation date is not reported therefore it is unclear which COP would be relevant. Assuming CHP refers to the latest 2016 COP, it can be deduced that the Legionella sampling result was <10 cfu/mL and the Heterotrophic Colony count (also known as the plate count) sampling was <100 000 cfu/mL.
The CHP report concludes with a total of 27 cases for 2020, compared with 105 cases in 2019, which equates to 25% of cases in 2019 cases.
UPDATE 6 March 2020
EMSD.gov.hkissued a press release for its regular Legionella testing [link] on 6 March 2020 with routine and epidemiological investigation information, for the latter, in the attachment annex 2 [link] titled Building locations of fresh water cooling towers detected with total legionella count at/above upper threshold (1,000 cfu/ml) with nuisance notices issued under PHMSO, the annex states that the MTR Choi Hung Station had a nuisance notice issued showing total 1700 cfu/ml Legionella count (above the action level).