To the Editor—Legionnaires’ disease (LD) is mainly transmitted by inhalation of infectious aerosol, while aspiration of contaminated water is another possible mode of transmission.Reference Cunha, Burillo and Bouza ^{1 –} Reference Johnson, Yu and Best ³ We report 3 LD cases with Legionella pneumophila (Lp) isolated in water samples from water dispensers with an ultraviolet (UV) sterilizer and a filter.

Legionnaires’ disease is a notifiable infectious disease in Hong Kong. The Centre for Health Protection conducts epidemiological investigations for all cases and carries out environmental investigations according to local protocols. Water samples for Legionella culture and Legionella sequence-based typing of Lp isolates from human and water samples are performed as required.

Patient 1 was a 59-year-old bed-bound male patient with malignant brain tumor. He had been staying in hospital A for management of his malignancy since mid-December 2015. He presented with oxygen desaturation on June 8, 2016. On June 11, 2016, his tracheal aspirate was positive for Lp (nonserogroup 1) DNA but was negative for Legionella by culture.

The room where he stayed in the hospital had a water dispenser with a UV sterilizer and a filter, and a shower. He did not drink water from the water dispenser, but his helper used unboiled cold water from the water dispenser and the shower to perform sponge bathing and face washing for him. A cold-water sample from the water dispenser was positive for Lp (non-serogroup 1) at 0.4 colony-forming units (CFU)/mL. In addition, 2 hot-water samples from the shower were positive for Lp (non-serogroup 1) at 3.1 and 32.0 CFU/mL, respectively (Table 1). Legionella pneumophila isolates from the 3 water samples were all sequence type 583 (ST583), which is very rare in Hong Kong. Only 5 of the 7 alleles were amplifiable from this patient’s tracheal aspirate, and they were identical to the corresponding alleles for ST583. The exact source of infection was undetermined because water samples from different sites were positive with the same sequence type.

TABLE 1 Environmental Water Samples Positive for Legionella pneumophila Associated With 3 Cases of Legionnaires’ Disease, Hong Kong

NOTE. Lp non-1, Legionella pneumophila (non-serogroup 1); ST, sequence type; Lp-1, Legionella pneumophila serogroup 1.

Patient 2 was a 90-year-old female with multiple medical illnesses who was admitted to hospital B on March 14, 2017, for intestinal obstruction; surgery was performed on March 17. She developed shortness of breath on March 23 and was transferred to another hospital for management on April 11. On April 12, her urine was positive for Lp-1 antigen. Endotracheal aspirates on April 12 and 13 were negative for Legionella by culture and polymerase chain reaction.

The room she stayed before LD onset had a water dispenser with a UV sterilizer with a filter, a water tap, and a shower. She reported that she drank unboiled cold water from the water dispenser and that she had used the shower for bathing. Furthermore, 2 cold-water samples from the water dispenser were positive for Lp-1 at 0.1 and 1.6 CFU/mL, respectively. No molecular typing was done because of the negative clinical samples and the source of infection remained undetermined.

Patient 3 was a 49-year-old female with hematological malignancy who was admitted to hospital C on August 12, 2017, for pneumonia and had intermittent fever after admission. She was discharged on September 11 and was admitted to another hospital on September 13. On August 29, her sputum was positive for Lp-1 DNA, and on September 13, her bronchoalveloar lavage culture was positive for Lp-1. She had stayed in multiple rooms located on different floors of hospital C. Cold drinking water was provided in pots supplied by the water dispenser in the pantry on that floor. The water dispenser was equipped with a UV sterilizer and a filter. The patient reported that she drank the pot water provided without boiling. A cold-water sample from the water dispenser in the pantry on one of the floors on which she had stayed was positive for Lp-1 (0.2 CFU/mL). The Lp-1 isolates from the patient and the water sample from the water dispenser were both ST1, the most prevalent environmental sequence type in Hong Kong. In this case, the patient’s onset of LD was uncertain, and the source of infection was undetermined.

The use of water dispensers equipped with different types of water treatment devices has gained popularity. Ultraviolet light has been reported as an effective means for disinfection against Legionella in water systems.Reference Hall, Giannetta, Getchell-White, Durbin and Farr ⁴ In our cases, the UV sterilizers claimed to deliver a UV dosage of 30 mJ/cm² or more, which is greater than the reported dosage require to inactivate Lp.Reference Antopol and Ellner ⁵ However, Lp was still recovered from cold-water samples from these water dispensers.

Failure to eradicate Legionella in water from these water dispensers can be multifactorial. The point-of-entry application of UV disinfection does not allow eradication of Legionella within the biofilms distal to the point of entry.Reference Lin, Stout and Yu ⁶ Moreover, UV disinfection provides no residual protection and regrowth of Legionella in the biofilm layers of scale, and accumulated debris may allow recolonization.Reference Liu, Stout, Tedesco, Boldin, Hwang and Yu ⁷

Immunosuppression is a well-established risk factor for LD.Reference Cunha, Burillo and Bouza ^{1 ,} Reference Lanternier, Ader, Pilmis, Catherinot, Jarraud and Lortholary ⁸ Studies have shown that bed bathing, use of nasogastric tube, and surgery are risk factors for nosocomial LD,Reference Blatt, Parkinson and Pace ^{2 ,} Reference Johnson, Yu and Best ^{3 ,} Reference Marrie, Haldane and MacDonald ⁹ and aspiration of contaminated water is a possible mode of transmission for Legionella.Reference Blatt, Parkinson and Pace ^{2 ,} Reference Johnson, Yu and Best ³ Our findings provide evidence that cold water from these water dispensers is not free from Legionella, but its association with LD could not be confirmed. However, it is prudent to advise immunocompromised patients, particularly those who are at high risk of aspiration, to avoid drinking cold water from these water dispensers without boiling. Moreover, hospitals should avoid installing these water dispensers in areas that serve a large number of immunocompromised patients.