GERMS OF THE GREAT OUTDOORS
From Rural, Remote, and Wilderness Medicine, sponsored by the University of California, Davis, Health System,
Departments of Emergency Medicine and Continuing Medical Education
Robert W. Derlet, MD, Professor, Department of Emergency Medicine, University of California, Davis, School of
Medicine
| INFECTIONS FROM DIRT AND DUST
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| Bacteria: inhaled; inoculated via cuts
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 | Tetanus: many species of Clostridium contained in dirt, most of which people’s natural immunity can handle
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| Acinetobacter: gram-negative bacteria cause cellulitis in wounds contaminated by soil; resistant to most antibiotics;
consider in patients with wound infection who are becoming septic; grows slowly in blood cultures; consult infectious
disease expert
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| Erysipelothrix: wound inoculation may cause cellulitis; responds well to penicillins, cephalosporins, and clindamycin;
probably underdiagnosed
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| Anthrax: of total of 12 cases, 6 cases of inhalation anthrax in United States in 2001; 100,000 skin infections in central
Asia during same year (exposure to dirt contaminated by animal that died from anthrax); responds well to antibiotics;
presents as flu-like illness; patients may stay home untreated; if patient presents septic, look for gram-
positive organisms in buffy coat of blood sample
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| Tularemia: found in hay as well as dirt and dust; transmitted by fly bites, tics, mosquitos, cat bites, aerosolization of
contaminated dirt; suspect in patients who present with pneumonia in areas of newly tilled land; symptoms include
fever, chills, and malaise; treated empirically with doxycycline
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| Coxiella burnetii (Q-fever): worldwide disease; organism found in droppings of cattle, sheep, goats, and horses;
can be inhaled in dust; symptoms include fever, cough, and pneumonia; patients typically treated empirically
with doxycycline, and organism never known
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| Psittacosis: carried by birds, namely, turkeys, ducks, chickens, and pigeons; birds may not be sick, but inoculate
dirt and dust
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| Lassa fever virus: found in central and western Africa; carried by rodents; excreted in droppings; fair number of
people have asymptomatic disease; hemorrhagic fever occurs in only 5% (high mortality)
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| South American Arenavirus: excreted in rodent droppings; people on farms and fields at risk for exposure; health
care personnel at risk of catching disease from patients
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| Hanta virus: carried by deer mice (not necessarily sick); long incubation period (up to 8 wk); patients present with 3
days of fever and myalgias and may return hypotensive with dyspnea, pulmonary edema, and high white blood cell
(WBC) count; high mortality; no good antiviral agent; serologic diagnosis with IgM testing fairly specific and accurate;
can use extracorporeal circulation to support patients through severe pulmonary edema; geographic
distribution—carried by 10% of deer mice in California, 10% to 50% in Sierra Nevada counties; susceptibility—
difficult for humans to acquire; only patients with immune defect get this disease; clinical clues—include hemoconcentration,
increased hematocrit, WBC count with left shift, abnormal lymphocytes, decreased platelets, elevated
liver function tests; unclear if contagious person to person; South American Hanta virus contagious among
hospital workers; sensitive to UV radiation
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| Lymphocytic choriomeningitis virus: widely underdiagnosed; flu-like syndrome; acquired through aerosolized
mouse droppings; patients present with fever, headache, and malaise; goes unrecognized in most cases; organism
not sensitive to sunlight
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| Respiratory enteric orphan virus (reovirus): ubiquitous in nature, animals, and humans; most humans in United
States have antibodies to this virus; patients present with upper respiratory infection (URI)-type symptomatology;
often undiagnosed
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| Fungi: ubiquitous in nature; humans generally immune to fungal infection; patients with weakened immunity (eg,
from chemotherapy, disease) susceptible; study looked at houses that should not have mold and found up to 1000
colony-forming units/m3 , regardless of season; most acquired through inhalation, resulting in pneumonia; most
cases treated empirically (doxycycline and other common first-line agents do not work); diagnostic dilemma in
most cases
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| Coccidioidomycosis: common problem after major dust storm; patients present with fever and cough; some patients
nearly asymptomatic; others develop severe illness and pneumonia; amphotericin commonly used to treat;
patients with immune defect develop systemic disease and must be repeatedly treated with amphotericin
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| Paracocci: no relationship to coccidioidomycosis; yeast-like infection confined to jungle areas of Central and South
America; chronic illness may develop over months; patients may present with weakness, fever, and cough; may
need to go back in history as much as 20 yr
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| Aspergillus: found everywhere; Aspergillus fumigatus most common human pathogen (problem in grain silos; produces
aflatoxin)
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| Blastomycosis: common fungus seen in shady, moist, river areas; incubation may take several weeks; presentation includes
fever, cough, and pneumonia; commonly treated with empiric antibiotics upon first presentation but fails to
improve; diagnosed with sputum culture or bronchoscopy; in other parts of world, spreads systemically to skin and
bones, and patients may present with weakness and skin lesions (more common in tropical regions)
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| Cryptococcus: yeast-like fungus; ubiquitous in dust, mostly planted there by pigeons and other birds; may cause
meningitis in immunosuppressed patients
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| Histoplasmosis: organism found in soil from bird droppings; may resolve spontaneously or may get worse and require
diagnosis
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| Rural: Q-fever, tularemia, psittacosis, clostridia; if abroad, Buruli ulcer, Hanta virus, Melioidosis, Arenaviruses
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| Wilderness: Hanta virus and some fungi
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| WILDERNESS WATER: IS IT SAFE TO DRINK?
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| Low-risk water: high-altitude lakes and streams where little or no permanent human settlement or farming; only 2
pathogens found, namely Escherichia coli and Yersinia enterocolitica
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| Speaker’s research: collected >500 samples of water in wilderness areas of Sierra Nevada; ≈10% had E coli or
other coliforms, primarily downstream from grazing cattle and heavy pack animal use; backpacker use not correlated
with contaminated watershed; Y enterocolitica found in many lakes above 10,000 ft; suspect contamination
by birds flying over; only one third of Yersinia species pathogenic in humans
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| Bacteria: must be present in water for healthy ecosystem; break down toxic compounds in air that dissolve in water;
ingested by plankton and protozoa; if no bacteria present in stream or lake, speaker would suspect it was poisoned
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| E coli: most strains nonpathogenic; all humans and animals have E coli in gut; O157:H7—excreted by healthy cattle;
present in <1% of range cattle, 30% to 40% of stockyard cattle; press does not differentiate O157:H7 from
other strains; most people who acquire infection experience self-limited colitis and bloody diarrhea; children at
risk for hemolytic-uremic syndrome; O121—produces Shiga toxin; can cause hemolytic-uremic syndrome; most
laboratories cannot differentiate species containing Shiga toxin from those that do not; may need to send samples
to Centers for Disease Control and Prevention (CDC)
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| Yersinia: excreted by birds, rodents, and farm animals; one third of subtypes pathogenic for humans; causes diarrhea
and abdominal pain; treat patients who are sick with quinolones
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| Moderate risk: farmland runoff, municipalities that have reasonable sewer systems; organisms found include E
coli, Yersinia, Giardia, Cryptosporidium, Campylobacter, Salmonella, and Leptospira
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| Giardia: low infective dose (10-25 cysts); cysts can survive months; outbreaks seen in mountain resorts as result of
septic tanks being too close to water wells; incubation period 1 to 3 wk or longer; patients present with foul-
smelling diarrhea, bloating, fever, and malaise; if only worried about Giardia, obtain direct immunofluorescence
test rather than ova and parasites (O and P; takes many days and studies to exclude all possible parasites); most
Giardia in Sierra imported from livestock over past 150 yr, rarely present in wild animals; metronidazole
(Flagyl) for 7 days standard treatment; quinacrine, tinidazole (2-g single dose), and nitazoxanide (Alina) also effective
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| Cryptosporidium: resistant to most halogens, so not killed by municipal water purification systems; multiple subtypes
infect animals and humans, although not all virulent; immunosuppressed people and children at higher risk;
in most cases patients have self-limited diarrhea; some patients develop dehydration, become more ill, and require
hospitalization; nitazoxanide efficacious
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| Salmonella: water and food-borne bacteria; multiple subtypes; animal and human reservoir; short incubation period
(easier to trace); species that causes typhoid fever worse form; more commonly found in imported food; new
vaccine now available for patients planning travel to high-risk areas (small percentage of patients become nauseated;
effective for 5 yr)
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| Leptospira: probably more common than suspected; found in farm and wild animals; found in streams in Hawaii and in
estuaries of San Francisco Bay; low infective dose; fever, myalgias, renal failure, and, in some cases, cardiovascular
collapse; causes headache, chills, vomiting, and diarrhea; antibiotics efficacious when given within first 2 days after
onset, but not after 7 days; self-limited in most cases
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| High risk: everything discussed so far plus Vibrio, rotavirus, Calicivirus, Echovirus, hepatitis, and poliovirus
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| Cholera: endemic throughout South America, Asia, and parts of Africa; acquired through water; requires large infective
dose; treat with salt and glucose solutions
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| Vibrio parahaemolyticus: common marine organism; found in salt and fresh water; can cause severe diarrhea and
vomiting; found in raw oysters; requires large infective dose; some species more virulent and aggressive
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| Rotavirus: can infect older adults; most common cause of waterborne disease in children in Africa; found in wells;
causes severe diarrhea, dehydration, and death
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| Norwalk virus: calicivirus; found on cruise ships; stable in environment and on fomites; very infective; problem in
water systems; causes abdominal cramps, diarrhea, vomiting, fever (in 50%); severe dehydration major problem;
incubation 1 to 2 days
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| Management of diarrhea and vomiting: give antibiotics to patients who look sick; patients with symptoms
who have history of travel may benefit from fluoroquinolone therapy
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| Purifying water: boil for 10 min in high-risk areas; in lower-risk areas, required only that water be brought to boil;
most water purifiers effective for protozoa and bacteria; new-generation filters can filter some viruses, but clog
more easily; use few drops of bleach, iodine, or other halogen (some pathogens take longer dwell time than others);
halogens work faster when water warm; some protozoa not neutralized by halogens
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| Solar irradiation: in one study of water from sewage treatment plant containing 500,000 E coli/qt, solar irradiation
killed all coliform bacteria (higher temperature, ie, 50°C, may have been contributing factor)
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| Safest water: top 6 in of lake that has had sun shining on it all day contains fewest coliforms
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Educational Objectives
| The goal of this program is to educate the listener about infectious pathogens found in dirt, dust, air, and water. After
hearing and assimilating this program, the clinician will be better able to:
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| 1. List the most common bacteria found in dirt and dust.
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| 2. Name 3 viruses found in dirt and dust, and describe their epidemiology.
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| 3. Discuss 3 fungi that are common to dirt and dust.
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| 4. Describe watersheds that are considered low-, moderate-, and high-risk in their safety for drinking.
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| 5. Illustrate how to purify water in a wilderness setting.
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Discussed on This Program
Acetaminophen (N -acetyl-P -aminophenol; APAP) (many trade names)
Amphotericin B [Amphocin, Fungizone Intravenous]
Azithromycin [Zithromax, Zmax]
Ciprofloxacin [Ciloxan, Cipro, Proquin XR]
Clindamycin (many trade names)
Doxycycline (many trade names)
Ibuprofen [Motrin, many others]
Metronidazole [Flagyl, others]
Nitazoxanide [Alinia]
Quinacrine HCl
Tinidazole [Tindamax]
Programs of Related Interest
Jong EC: Travel medicine. Audio-Digest Family Practice 52:06(Feb 14), 2004; Klein JR, Schechtman A: Strategies
for surviving the summer. Audio-Digest Family Practice 53:24(Jun 28), 2005; Lane AT, Caldwell AL:
Summer hazards. Audio-Digest Pediatrics 51:08(Apr 21), 2005.
To Order, Contact Subscriber Service (1-800-423-2308)
Suggested Reading
Centers for Disease Control and Prevention (CDC): Norovirus outbreak among evacuees from hurricane
Katrina--Houston, Texas, September 2005. MMWR Morb Mortal Wkly Rep 54:1016, 2005; Chalupka S: Tainted
water on tap: what to tell patients about preventing illness from drinking water. Am J Nurs 105:40, 2005; Derlet
RW et al: An analysis of human pathogens found in horse/mule manure along the John Muir Trail in Kings Canyon
and Sequoia and Yosemite National Parks. Wilderness Environ Med 13:113, 2002; Derlet RW et al: An analysis of
wilderness water in Kings Canyon, Sequoia, and Yosemite national parks for coliform and pathologic bacteria. Wilderness
Environ Med 15:238, 2004; Derlet RW et al: Coliform and pathologic bacteria in Sierra Nevada national
forest wilderness area lakes and streams. Wilderness Environ Med 15:245, 2004; Derlet RW et al: Coliform bacteria
in Sierra Nevada wilderness lakes and streams: what is the impact of backpackers, pack animals, and cattle? Wilderness
Environ Med 17:15, 2006; Fossler CP et al: Herd-level factors associated with isolation of Salmonella in a
multi-state study of conventional and organic dairy farms I. Salmonella shedding in cows. Prev Vet Med 70:257,
2005; Lehr MA et al: Associations between water quality, Pasteurella multocida, and avian cholera at Sacramento
National Wildlife Refuge. J Wildl Dis 41:291, 2005; Poullis DA et al: The characterization of waterborne-disease
outbreaks. Rev Environ Health 20:141, 2005; Rangel JM et al: Epidemiology of Escherichia coli O157:H7 outbreaks,
United States, 1982-2002. Emerg Infect Dis 11:603, 2005; Reavis C: Rural health alert: Helicobacter pylori
in well water. J Am Acad Nurse Pract 17:283, 2005; Weber CJ: Update on travelers’ health. Urol Nurs 25:392,
2005; Wilson ME: Diarrhea in nontravelers: risk and etiology. Clin Infect Dis 41 Suppl 8:S541, 2005.
Faculty Disclosure
In adherence to ACCME guidelines, the Audio-Digest Foundation requests all lecturers to disclose any significant financial
relationship with the manufacturer or provider of any commercial product or service discussed. For this issue,
the speaker reported no conflict.
Dr. Derlet was recorded October 20 and 22, 2005, in San Francisco, CA, at Rural, Remote, and Wilderness Medicine,
sponsored by the University of California, Davis, Health System, Departments of Emergency Medicine and Continuing
Medical Education. The Audio-Digest Foundation thanks the speaker and the sponsors for their cooperation in the production
of this program.
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