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Epidemiologic Notes and Reports Otitis due to Pseudomonas aeruginosa Serotype 0:10 Associated with a Mobile Redwood Hot Tub System -- North Carolina

From March 19 to April 2, 1982, six cases of Pseudomonas aeruginosa, serotype 0:10, infection occurred following common exposure to a hot tub in Orange County, North Carolina. Clinical illness included severe hemorrhagic external otitis, which, although commonly associated with swimming pools, has not been previously reported in the literature for whirlpool/spa settings.

Among 24 members of a university coeducational fraternity who used the implicated tub from March 26 to 29, two had simple dermatitis, and four developed severe external otitis, one of whom, a 19-year-old male, had concurrent cellulitis of the chest wall and thigh. He was hospitalized and treated with intravenous tobramycin for 4 days. His infection began as an area of erythema approximately 1-1/2 inches in diameter below the left nipple, accompanied by tender left axillary adenopathy and a pustule below the right nipple. The patient also noted severe pain and drainage from his left ear. Cultures from the chest pustule and the draining left ear were positive for P. aeruginosa serotype 0:10 (resistant to cephalothin, ampicillin, tetracycline, and trimethoprim-sulfamethoxazole and sensitive to gentamicin and carbenicillin). His symptoms began 48 hours after last exposure to the tub. The three other persons with severe external otitis that began within 48 hours of last exposure to the tub visited the student health service for treatment. In two of those, disease was bilateral and was associated with profound erythema or bloody discharge. The first had onset on March 27; the other, with onset on March 29, had a positive culture of ear drainage for P. aeruginosa of the same resistance pattern as the 19-year-old male. Neither responded to topical antibiotics, but both were treated successfully with intramuscular gentamicin.

A survey of fraternity members showed an association of illness with exposure to the tub, which was rented and used from March 26 to 29. Of 15 students who responded to a questionnaire, five (described above) met the case definition of ear infection or skin rash developing within 7 days after exposure to this tub. Total duration of exposure to the tub over the 4-day period was significantly associated with illness. Patients had a mean duration of 10.2 hours exposure; non-patients had a mean duration of 5.1 hours exposure (t = 2.83, p 0.02). Only one of the five patients had exposure to another recreational water supply, spa, or whirlpool.

The hot tub in question was a portable, self-contained unit constructed of redwood; it measured approximately 6 feet in diameter by 4 feet deep, and held 700 gallons. It was mounted on a trailer for easy transport and had terraced observation decks above and below. The tub was filled with city water, supplied through a garden hose. A recirculation system with a pump, hair trap, dual filter, continuous-feed brominating system, air-introduction port (for a bubbling effect), and propane-fueled heating system were built in. Water could be drained to surrounding areas through a port in its base. Temperature was usually maintained at 104 F (40 C).

Inspection and culturing of the tub on April 15, after a previous night's usage at another fraternity, showed a pH 7.6 and free bromine level of 0.5 parts per million (ppm). Of 12 environmental swabs of the tub, four were positive for P. aeruginosa serotype 0:10. No other serotypes were identified in the specimens. The positive sites included a recirculation port, two areas of the dual filter, and filter intake line.

Procedures involved in maintaining and using the tub were reviewed. Usage peaked during the four evenings, when 15 or more persons at a time were in the tub. Despite written instructions to check the free-bromine level every four hours, water sampling was performed only once before use each day. The tub was emptied and rinsed with water from a garden hose daily, and filters were sprayed with water on March 27 and 28. No hyperbromination or scrubbing of internal surfaces was performed. Reported by J McCutchan, MD, Student Health Service, University of North Carolina, WA Rutala, PhD, Dept of Epidemiology, University of North Carolina Memorial Hospital, R Holdway, T Laws, Orange County Health Dept, Chapel Hill, N King, MP Hines, DVM, State Epidemiologist, North Carolina State Dept of Human Resources; Field Svcs Div, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: This episode points out the public health risks associated with a hot tub system rented by individuals not trained in its appropriate maintenance and monitoring of pH and bromine (or chlorine) levels. Prior outbreaks of P. aeruginosa dermatitis associated with heated whirlpools have generally involved serotype O:11. In most cases, rash was self-limited and resolved within 7 days of onset without antimicrobial therapy. Otitis occurred at low frequencies in two outbreaks (1,2). The illness reported here is unusually severe for pool-associated P. aeruginosa infection, and investigations indicated duration of exposure as a significant risk factor. After reviewing guidelines for hot tub use, hyperchlorination of the hot tub was instituted before each use. Whether serotype 0:10 may represent a more invasive form of P. aeruginosa or whether other factors such as prolonged exposure may have contributed to the development of this spectrum of infection is undetermined at present.

Conditions relating to the design and use of whirlpools and hot tubs present certain sanitation problems often favorable for P. aeruginosa (3). Water temperature is usually 104 F-108 F (40 C- 42.2 C), and a high bather load often markedly reduces free-chlorine and -bromine levels. Aeration and agitation of water can also quickly deplete disinfectant residuals. Chlorine or bromine should be maintained at a free residual level of 1.5 ppm. Filtration equipment should be inspected and serviced regularly (4).


  1. McCausland WJ, Cox PJ. Pseudomonas infection traced to motel whirlpool. Journal of Environmental Health 1975;37:455-9.

  2. Washburn J, Jacobson JA, Marston E, Thorsen B. Pseudomonas aeruginosa rash associated with a whirlpool. JAMA 1976;235:2205-7.

  3. Kush BJ, Hoadley AW. A preliminary survey of the association of Pseudomonas aeruginosa with commercial whirlpool bath waters. Am J Public Health 1980;70: 279-81.

  4. Environmental Health Services Division. CDC. Suggested health and safety guidelines for public spas and hot tubs. Atlanta: U.S. Department of Health and Human Services, CDC 1981.

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