Abstract
Introduction
Diarrhea is a common problem among long-distance backpackers, ranging in overall incidence from 11–56% as reported by previous studies on the Appalachian Trail and Long Trail. Differences in age, sex, and regularity of standard backcountry hygiene recommendations and practices have been shown to significantly affect the incidence of diarrhea. No study to date has investigated these trends among long-distance backpackers on the John Muir Trail (JMT) in the Sierra Nevada mountain range of California.
Methods
Retrospective analysis of online survey data gathered from long-distance backpackers who attempted a JMT trek in 2014. Data were assessed for the significance of variables that might contribute to the incidence and severity of on-trail diarrhea.
Results
Of 737 valid responders, 16.4% reported experiencing diarrhea (82% with minimal/mild severity; 18% with significant severity). Regular hand sanitizer use was significantly correlated with more severe diarrhea (
Conclusions
JMT backpackers have a comparatively lower incidence of diarrhea than backpackers on other major long-distance backpacking routes in the United States. Most JMT backpackers follow standard backcountry hygiene recommendations, including regular filtration or treatment of drinking water. No statistical significance was found between the incidence of diarrhea and compliance with standard hygiene recommendations. Regular hand sanitizer use was significantly correlated with more severe diarrhea but was not associated with incidence. There was no significant difference in compliance with standard backcountry hygiene practices between regular and infrequent hand sanitizer users.
Introduction
The John Muir Trail (JMT), a world-famous long-distance backpacking trail in the Sierra Nevada mountain range of California, is often compared with other long-distance backpacking trails in the United States, such as the Appalachian Trail (AT), which stretches from Georgia to Maine, and the Long Trail in Vermont. In the past 25 years, several studies have found significant correlation between long-distance backpacker demographics and on-trail hiking behaviors and specific morbidities encountered during such activities. In these previous analyses, diarrhea was consistently regarded as a significant morbidity among long-distance backpackers, ranging in overall reported incidence from 10.7 to 56%, depending on the year and geographical region surveyed. 1 –6 Furthermore, within previous AT studies, the incidence of diarrhea was found to differ among particular populations of backpackers, with variables including age, sex, and regularity of following standard backcountry recommendations for hand hygiene, dish washing, and water filtration practices. 4 –6 However, no studies to date have attempted to determine the incidence of diarrhea and the potentially implicit variables among long-distance backpackers in the Sierra Nevada or, specifically, on the JMT.
Methods
Study Design
This is a retrospective analysis of online survey data gathered from long-distance backpackers who attempted a JMT trip in 2014. Backpackers were recruited through JMT-related message boards on Yahoo! Groups and Facebook as well as through in-person recruitment on the JMT. Participants completed an online 60-page, 87-question posthike survey after the 2014 hiking season. The online survey and the original data were maintained by a private JMT enthusiast who granted permission for use of the data for this study. Institutional review board approval through the University of California, San Francisco was obtained for retrospective analysis of the survey data.
In the survey, participants were informed that the data may be used for future research and opted into the study by submitting the survey. All data were de-identified by replacing the personal e-mail used to link survey answers with a nonidentifying survey participant identification number. Survey data pertaining to backpacker demographics, on-trail hygiene practices, and diarrhea incidence and severity were analyzed.
Setting and Subjects
The JMT is a long-distance backpacking trail in the Sierra Nevada mountain range of California, stretching from Yosemite Valley to Mount Whitney, the highest point in the contiguous United States. It passes through some of the crown jewels of America’s park system: Yosemite, John Muir and Ansel Adams Wildernesses, Kings Canyon, and Sequoia National Parks. This 338- to 354-kilometers (210 to 220 miles)-long trail (depending on one’s starting point) is generally accessible from July through September. For almost all of its length, the trail is in the High Sierra backcountry (above 2438 meters [8000 feet]) and within designated wilderness areas that require permits from either the National Park or Forest Service. Most backpackers attempt to through-hike the entire length of the JMT hike from north to south and complete the trek over the course of several weeks, with several resupply stops along the way. For the majority of its length, backpackers must obtain water from various trailside lakes and streams.
Participants who completed the survey included long-distance backpackers who had attempted some portion of the JMT in 2014. A total of 769 surveys were collected. In an effort to avoid inclusion of data from “day hikers” or “weekend backpackers” in our desired study population, respondents who completed less than 2 days’ distance of total backpacking (for which a “day” was considered the average amount of miles hiked per day for all backpackers) were excluded. Seventeen backpackers were eliminated based on this criterion. Additionally, respondents who did not complete sections of the survey needed for data analyses were also excluded, which removed 15 more backpackers. Following these exclusion criteria, our study comprised a population of 737 valid respondents from the 769 total received surveys.
Study Data
From the 87-question survey, we analyzed response data associated with the following demographic variables: age, sex, prehike body weight, prehike physical activity (hours/week), prehike self-assessed physical condition, previous hiking or backpacking experience (days in previous 10 years), solo or group backpacking itinerary, on-trail average pack weight, on-trail hygiene compliance (water filtration/treatment, hand hygiene, etc), and posthike difficulty assessment (Table 1). Self-reported data on the incidence and severity of diarrhea were also examined, where severity was reported on a scale from 1 (minimal) to 5 (severe).
Backpacker demographics from 2014 hiking season (n=737)
Data Analysis
Data analysis was performed by transferring the participants’ responses from a Microsoft Office Excel spreadsheet into SPSS statistical software. Statistical significance was set at
In running statistical analyses, compliance variables and diarrhea were considered as both continuous and dichotomous categorical data (compliance recoding to categorical: 0–2 = low compliance, 3–5 = high compliance; diarrhea recoding to categorical: 0 = diarrhea negative, 1–5 = diarrhea positive). When all variables were continuous, linear regressions were used to show contribution to diarrhea severity, and bivariate correlations were used to show any association between one compliance variable and diarrhea. When compliance variables were continuous and diarrhea was categorical, logistic regressions were used to determine whether any of the compliance variables contributed to diarrhea outcome. When all variables were categorical, χ2 and Fisher exact tests were used to test whether the observed relationships were significant. When compliance variables were categorical and diarrhea was continuous, t tests were used to determine if there was a significant difference in diarrhea severity between those who complied with a single compliance variable and those who did not.
Results
After application of exclusion criteria, our study comprised a population of 737 valid responders. Of this backpacker population, 16.4% (n = 121) reported experiencing diarrhea at some point on the JMT. Although a majority (82%) of backpackers with diarrhea reported minimal or mild severity, 18% reported having significant diarrhea (rated a 3 or greater), with 5% reporting severe diarrhea (rated a 5). When all hiker demographic variables were combined into a single regression model, there were no significant findings regarding incidence or severity of diarrhea. When each demographic variable was assessed through independent sample t tests, the hiker characteristics of height (
Independent sample t tests of diarrhea incidence and bivariate correlations of diarrhea severity with both hiker demographics and hygiene compliance
Incidence assessed as categorical (positive/negative) with hygiene variables recoded as categorical (0–2 low compliance, 3–5 high compliance). Severity assessed as continuous (1–5) with hygiene variables left as continuous.
Regularity of compliance with standard backpacking hygiene recommendations and practices was also analyzed against diarrhea incidence and severity. The only significant positive correlation involved regularity of hand sanitizer use and severity of diarrhea. Those who used hand sanitizer more regularly (rated a 3 or greater) had significantly more severe diarrhea than those who did not use hand sanitizer regularly (
Further analyses revealed that regular hand sanitizer use overall was not correlated with having a significantly higher incidence of diarrhea when assessed categorically. Additionally, among all backpackers, regular hand sanitizer users were more likely to bury their waste, pack toilet paper, and filter water for cleaning purposes than those who did not use hand sanitizer regularly (
Drinking water filtration or treatment regularity and incidence of diarrhea were also examined. Most backpackers on the JMT filtered or treated their drinking water at least regularly (88%; n=655), with 18% of that group reporting diarrhea of any severity. Backpackers who practiced infrequent filtration or treatment of drinking water (12%; n=82) reported a diarrhea incidence of 10%. There was no statistical significance between regularity of water filtration or treatment and diarrhea incidence or severity (Table 2).
Discussion
Our study suggests that diarrhea affects a small percentage (16.4%) of JMT long-distance backpackers, with only 5% of those hikers reporting severe diarrhea. This is in contrast to the higher incidence rate of 56% reported on the AT (Table 3).5,6 Regarding demographics, our study found no significant difference in JMT backpacker age, sex, or prior hiking experience as related to the incidence of diarrhea. The average age of JMT backpackers was 43 years. Comparatively, AT backpackers who did not experience diarrhea were significantly older than those hikers who did experience diarrhea (39.1 vs 31.4 years). 6 Additionally, AT backpackers over the age of 30 years were found to have a reduced occurrence of diarrhea and better mean hygiene scores for handwashing after urination or defecation. 6 Although our JMT study population was on average older than that examined on the AT, we found no significant difference in hiker demographics associated with hygiene practice regularity. Interestingly, backpacker height, prehike weight, and posthike weight were significantly correlated with increased diarrhea incidence and severity, although a combined regression model of all demographics failed to reach significance. The finding that shorter, lighter backpackers were more likely to have diarrhea and to report more severe diarrhea than taller, heavier backpackers is certainly unusual and may be reflective of sampling error (type 1 error) when these demographics were analyzed independently.
Standard wilderness hygiene practices are an important aspect of backpacking preventative medicine. Backpackers on the JMT reported following hygiene recommendations, on average, “almost always,” although they reported washing their hands without soap more often than with soap. Interestingly, our study shows no significant difference in incidence or severity of diarrhea regardless of regular compliance with such hand washing practices. This contrasts with previous studies on the AT, where practicing “good hygiene”—defined as routine cleaning of cooking utensils with soap and warm water and cleaning hands after urinating or bowel movements—was associated with a significantly decreased risk of developing diarrhea. 6 In the Sierra Nevada, use of soap in the backcountry’s pristine streams and lakes has been shown to prompt conditions that lead to increased survival or growth of coliform bacteria, and recommendations against such practices have been made. 7 The “pack it in, pack it out” practice for all soiled toilet paper is the current gold standard for long-distance backpackers in the Sierra Nevada. Unfortunately, this practice may not be consistently applied by all JMT backpackers or day hikers, possibly leading to contamination of pristine water sources.
Fecal contamination of watersheds used as sources of water for long-distance backpackers poses a great threat for the potential development of pathogen-associated diarrhea. Pathogens such as
Backpackers are encouraged to filter and treat all water obtained from wilderness sources for drinking and cleaning purposes. Backpackers on the JMT reported filtering or treating drinking water on average “almost always” to “always,” with 88% filtering drinking water at least regularly. Our study did not find a significant correlation between water filtration or treatment regularity and diarrhea incidence or severity. This is in contrast to similar studies from the AT where the incidence of diarrhea was significantly greater among those who frequently drank untreated water from streams or ponds.5,6 Among backpackers on the AT who practiced regular treatment of drinking or dishwashing water with filtration or iodine methods, 45% still experienced diarrhea.6,7 This is in contrast to the 18% of JMT backpackers in our study who reported similar compliance with water filtration or treatment but still had diarrhea. This variability in the incidence of diarrhea between JMT and AT backpackers who regularly complied with water filtration or treatment standards may be due to a variety of factors, including substantially different trail distances and total time spent backpacking, geographical differences related to watershed patterns, snow melt in the Sierra, stock usage and proximity to water sources, previously described higher density of coliform bacteria and
Hand sanitizer use regularity on the JMT was also examined alongside other standard backcountry hygiene practices. Regular use of hand sanitizer resulted in a significantly higher reported severity of diarrhea, although regular hand sanitizer use overall was not correlated with a significantly higher incidence of diarrhea. Although we expected incidence to be unaffected by the use of hand sanitizer, the significant difference in severity of diarrhea between user groups was an unexpected finding. Alcohol-based hand sanitizers have been found to work equally well or even significantly better than handwashing with soap and water with respect to reduction of pathogenic bacteria in field settings similar to wilderness backpacking (eg, livestock barns, farms, and homes in developing nations).11,12 A previous study has also shown that hand sanitizer is equally efficacious on clean versus dirty or oily hands. 13 However, to our knowledge, there are no studies examining the effects of hand sanitizer use specifically with recreational backcountry activities. In the absence of comparable data, we considered that one possible explanation for the observed difference in severity of diarrhea may pertain to regular hand sanitizer users following other hygiene practices less stringently. However, further analyses revealed that regular hand sanitizer users demonstrated just as high a compliance with all other recommended standard backcountry hygiene practices as those backpackers not using hand sanitizer regularly (and for some practices, significantly exceeded compliance regularity). Using hand sanitizer after toileting requires the backpacker to hold the sanitizer bottle with soiled hands, and if the bottle is not appropriately cleansed before being placed back into a backpack, it may result in other items being contaminated with coliform bacteria. How this may affect diarrhea severity but not incidence is unknown, and further research is needed to evaluate this hypothesis.
Study Limitations
As is the nature of retrospective survey studies, participant selection and recall bias are major limitations. The self-reporting nature of symptom severity has a great deal of subjectivity and may have artificially increased the number of backpackers reporting more severe diarrhea. Several backpackers also reported pre-existing conditions (eg, irritable bowel syndrome or inflammatory bowel disease) that may have exacerbated the reported incidence or severity of diarrhea. Soft stool resulting from diet-related changes while backpacking may have been interpreted as diarrhea by some backpackers. Along the JMT, there are several opportunities to dine just off trail at nearby cantinas and restocking points, whereby foodborne pathogens could have theoretically led to diarrhea. Although our exclusion criteria attempted to eliminate backpackers hiking less than 2 days’ average mileage, those backpackers acquiring diarrhea just before trip onset on the JMT may have had symptoms persisting past 2 days and may have been included in our study population.
Conclusions
Backpackers on the JMT have a comparatively lower incidence of diarrhea than those on other major long-distance backpacking routes in the United States. A majority of JMT backpackers follow standard backcountry hygiene recommendations, including regular filtration or treatment of drinking water. No statistical significance was found between diarrhea incidence and compliance with standard hygiene recommendations. Regular hand sanitizer use was significantly correlated with more severe diarrhea but was not associated with incidence. Additionally, regular hand sanitizer users showed no significant difference in compliance regularity regarding any of the other recommended standard backcountry hygiene practices.
Footnotes
Acknowledgements
Acknowledgments: The authors would like to extend particular gratitude to John Ladd for granting permission of use of his 2014 John Muir Trail Hiker Survey data, to Svetlana Bagdasarov for her assistance as liaison with the Institutional Review Board and coordinating meetings, and especially all past, present, and future JMT backpackers, who continue to inspire generations of hikers both old and new.
Author Contributions: Study concept and design (DJM, SJS); acquisition of the data (SJS); analysis of the data (AC); drafting of the manuscript (DJM, AC, SJS); critical revision of the manuscript (DJM, AC, SJS); approval of final manuscript (DJM, AC, SJS).
Financial/Material Support: None.
Disclosure Statement: None.
Submitted for publication May 2016.Accepted for publication December 2016.