Epidemiologic Notes and Reports Staphylococcal Infections among River Guides -- Tennessee, South Carolina, and North Carolina

On July 29, 1982, a private physician notified the Tennessee Department of Public Health (TDPH) of six cases of staphylococcal cellulitis among guides employed by a whitewater-rafting company at the Ocoee River in eastern Tennessee. Investigation revealed additional cases among employees at seven rafting operations in Tennessee, North Carolina, and South Carolina.

The first rafting company (Company A) employs approximately 150 persons, including 91 river guides, at sites on the Nantahala, French Broad, Ocoee, and Chattooga rivers. Twenty-three percent of guides are female; most guides are between 18 and 35 years of age. Seventy percent of guides have worked with the company for more than one season. All employees eat and sleep on-site in a communal-like setting, with mess halls, common bathing facilities, and simple wooden bunkhouses at each site, but do not normally share linens, towels, washcloths, clothing, or personal equipment. Employees are assigned randomly to different sites each week.

Twenty-three employees at the Ocoee site were examined. A case was defined as a person who reported lesions compatible with staphylococcal cellulitis, furunculosis, or abscess with onset between April 15 and August 1, 1982. Seven (33%) of 21 guides met this case definition; of these, four had received oral antibiotics, and one had been hospitalized. Employees reported that similar lesions had been common among guides for at least 3 years; many believed that assignment to the Chattooga River site in South Carolina was associated with increased risk of infection. Accordingly, the 20 employees at that site were examined; 12 (71%) of 17 guides met the case definition. At both the Ocoee and Chattooga sites, infections occurred exclusively on the lower extremities, predominantly the anterior lower legs and feet.

A case-control study was conducted of these 38 guides, using uninfected guides as controls. All employees at the Ocoee and Chattooga sites were interviewed, and nasal, palm, and wound cultures were obtained at the Ocoee site. Stepwise logistic regression analysis suggested that a positive culture result and increasing number of weeks worked this season were positively correlated with infection, while experience in prior seasons was protective. Four of six cases from the Ocoee site had had infected roommates, as compared with two of 14 controls.

Work records of these employees were analyzed by the number of weeks worked at each site, and total work weeks at each site were compared for cases and controls. The odds that a given work-week was contributed by a case rather than a control were 2.4 times higher at the Chatooga site than at the Ocoee (odds ratio 2.4, p 0.005). Many employees had not worked at one or more sites; attack rates for those employees with no exposure to certain river sites ranged from 50% to 66%, except for those never exposed to the Chattooga, for whom the attack rate was 28%. Based on the number of work weeks at that site, employees categorized as having low, medium, or high exposure to the Chattooga site had attack rates of 26%, 58%, and 67%, respectively (p

0.05). Typically, bunkhouses at the Chattooga site are 100% occupied, as compared with 80% at the Ocoee site, and guides at the Chattooga site spend 15% more time per week on the river. Investigation at the two sites failed to reveal any other differences in personnel, equipment, practices, or the challenges of the rivers likely to explain the differing infection rates.

No deviations from accepted standards of housing, food-handling, or hygiene likely to explain these high attack rates were identified. Accordingly, the investigation was extended to include other rafting companies.

Nine other commercial rafting companies operating on the Chattooga, Ocoee, or Nantahala rivers were identified, and interviews were conducted. Four operations had employees who met the case definition; all four had had employees placed on antibiotics, and two had had employees hospitalized. The five remaining operations reported no infections, antibiotic use, or hospitalization among their employees. Affected and unaffected companies at a given site utilized essentially the same techniques and equipment and rafted the same stretches of river at the same times and days. Seven of 12 operations had on-site, multiple-occupancy sleeping units, as well as other "communal" facilities. All seven "communal" sites and none of five "non-communal" ones reported staphylococcal infections and had had employees on antibiotics (p = 0.001); five of seven "communal" and none of five "non-communal" sites had had employees hospitalized for staphylococcal infections (p = 0.0265).

One other "communal" and one "non-communal" company operating on the Ocoee were selected for further investigation. Nine of 11 employees at the "communal" company (Company B) and 14 of 15 employees of the "non-communal" company (Company C) were interviewed, examined, and cultured as above. Two of nine employees at Company B were cases, as compared with no cases among 14 employees of Company C.

All culture specimens were routinely processed by TDPH laboratories, and isolates of coagulase-positive Staphylococcus aureus were phage-typed by CDC. S. aureus carriage rates were 56.5% at Company A, 88.9% at Company B, and 42.9% at Company C. Phage typing revealed several co-dominant phage types at Company A, two dominant phage types at Company B, and no pattern of phage types at Company C.

Employees at both affected and unaffected companies reported frequent skin abrasions caused by jamming their legs under the aft thwarts of the raft for stability. Accordingly, further studies were undertaken at Company A. Five of 27 rafts cultured before a trip were positive for S. aureus, as were 12 of 22 rafts cultured after a trip (odds ratio = 4.9, p 0.025). Eighteen rafts were cultured both before and after use. Three were positive for S. aureus before a trip, and two of these remained positive after the trip. Of the fifteen rafts negative before a trip, eight were positive after the trip (53% conversion) including three of three at the Chattooga site and five of 12 at the Ocoee site (p = 0.12). Two of seven rafts in storage over 72 hours were also positive for S. aureus.

Recommended control measures were routine hexachlorophene scrubs for all employees, active surveillance for new cases, prompt medical treatment, isolation of active cases, and improved management of linens and equipment. New cases have not been reported since instituting these measures. Reported by R Baron, MD, Benton Health Center, Benton, W Schaffner, MD, Vanderbilt University, F Hadley, MD, R Kelley, F Jordan, RH Hutcheson, Jr, MD, State Epidemiologist, Tennessee State Dept of Public Health; JN MacCormack, MD, MP Hines, DVM, State Epidemiologist, North Carolina State Dept of Human Resources; RL Parker, DVM, State Epidemiologist, South Carolina State Dept of Health and Environmental Control; Field Svcs Div, Epidemiology Program Office, Hospital Infections Program, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Epidemic staphylococcal disease is an unusual occupational hazard outside of health care settings. Outbreaks similar to this one are reported to have occurred among members of high school football teams, and to have responded to similar control measures. These reports, however, involved persons with direct, violent, physical contact.

In this report, several epidemiologic features apparently contributed to the spread of disease among the river guides. Whitewater rafting is a seasonal sport; each spring, as the guides arrive, strains of S. aureus are undoubtedly introduced into the group by human carriers. The guides' constant exposure to river rafts and the associated trauma to their shins and ankles provide sites for inoculation of the organism and subsequent infection. It is particularly noteworthy that some of the same strains of S. aureus infecting the guides were readily recoverable from rafts after several hours of alternate submersion in the river and drying in fresh air and sunlight, even when cultured as long as 72 hours after the raft was last used. S. aureus is known to be resistant to drying and to be recoverable from environmental sources, such as dust, for long periods of time; however, such environmental sources of S. aureus are not usually believed to be epidemiologically important in transmission of infection and disease, especially in comparison with the potential for transmission from human disseminators (including auto-inoculation).

If persistence of the organism on the rafts and direct inoculation of traumatized skin surfaces by this route were the only mechanism of transmission in this outbreak, differences in the frequency of disease among companies with "communal" and "non-communal" living arrangements or among different river sites would not be expected. Differences do exist for each of these factors, as well as for association of disease among roommates in the "communal" facilities. The "communal" living arrangements apparently altered the epidemiology of the disease, perhaps by facilitating the selection and maintenance of more virulent strains of S. aureus, by promoting frequent transmission of staphylococci among roommates, or by providing other means of transmission of the organism to traumatized skin sites, i.e., auto-inoculation. Although factors facilitating such transmission were sought, none was identified. Company A's practice of randomly and frequently rotating the employees may have disseminated the more virulent strains of S. aureus to all river sites used by the company.

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