These four scenarios were created to see how much you’ve learned in this module. The answers are for self-check only.
Detailed explanations with primary sources are provided regardless of your response. Take your time.
Priya
Priya is a 34-year-old woman who presents with a 12-day history of progressively worsening fever—initially low-grade, now 39.8°C—accompanied by headache, anorexia, and abdominal discomfort. She returned three weeks ago from visiting family in a rural region of India that had experienced severe flooding two months prior. On examination, she has relative bradycardia and mild hepatosplenomegaly. Blood cultures are ordered.
Which of the following best explains the climate-related mechanism most likely responsible for her illness?
Typhoid fever transmission is primarily through the fecal-oral route, via consumption of food or water contaminated with the feces of a carrier. Flooding overwhelms sanitation infrastructure and disperses fecal pathogens from sewage systems into previously protected drinking water and food supplies. This is the flooding dispersal mechanism. The clinical picture is consistent with typhoid fever: stepwise fever progression, relative bradycardia (pulse-temperature dissociation), and hepatosplenomegaly.
- The first option describes leptospirosis, a different pathogen using a different flooding mechanism.
- The third option describes the drought concentration mechanism, which is the opposite of what occurred here.
- The last option is inaccurate. Flooding disrupts healthcare access, but typhoid vaccine failure is not the mechanism of epidemic transmission.
Source: Waterborne Diseases That Are Sensitive to Climate Variability and Climate Change. N Engl J Med.
Nico
Nico is a 41-year-old man from a subsistence-farming community who presents with a three-month history of a symmetrical photosensitive rash on sun-exposed skin, intermittent diarrhea, and progressive confusion and memory impairment. His diet consists almost entirely of corn grown on his own farm. Caloric intake appears adequate. The region has experienced four consecutive above-average temperature growing seasons.
Which of the following climate mechanisms most directly explains his presentation despite adequate caloric intake?
This is the classic presentation of pellagra—the four Ds of dermatitis, diarrhea, dementia, and death if untreated—caused by niacin (vitamin B3) deficiency. Corn is inherently low in bioavailable niacin, which is why corn-dependent diets have long carried pellagra risk. Elevated CO2 adds a second stressor: It drives carbohydrate synthesis in crops while diluting micronutrient concentrations per gram, including B vitamins such as niacin. The CO2 dilution effect is the climate-related contributor this question highlights: The same dilution mechanism seen with iron and zinc, here producing a B-vitamin presentation that is clinically distinct but equally recognizable.
- The first option incorrectly invokes caloric deficit when the stem states caloric intake is adequate.
- The second option describes aflatoxin, which causes hepatotoxicity rather than the pellagra triad.
- The last option incorrectly attributes neurologic symptoms to cyanotoxin exposure without the water source change that mechanism requires.
Is there a source for this?
Hasan
Hasan is a 48-year-old man originally from rural Bangladesh who presents with a three-year history of gradually worsening peripheral neuropathy in a stocking-glove distribution, patchy hyperpigmentation of the trunk and extremities, and hyperkeratosis of his palms and soles. He immigrated to the United States twenty years ago and has no current occupational chemical exposure. He takes no medications.
Which addition to the social history is most likely to establish the environmental etiology of his presentation?
This is the classic delayed presentation of chronic arsenicosis—peripheral neuropathy, hyperpigmentation, and palmoplantar hyperkeratosis—from prolonged groundwater arsenic exposure. Bangladesh has some of the highest rates of naturally occurring groundwater arsenic contamination in the world.
Skin lesions may take 3–7 years to appear after initial exposure and can persist for decades; a patient who consumed contaminated well water in Bangladesh may present to a physician in the United States twenty years after immigration with the consequences of that past exposure.
The history question that unlocks this diagnosis asks specifically about water source during the years of exposure.
Occupational exposure to industrial chemicals or heavy metals is a legitimate consideration for peripheral neuropathy and hyperkeratosis—and should be asked about—but the stem already states no current occupational chemical exposure, making this the least informative addition in this clinical context.
The Hunger Vital Sign screens for food insecurity but does not address the environmental etiology of this delayed, chronic presentation. Asking about recent freshwater recreational activities would be relevant for leptospirosis or Naegleria fowleri but not for this symptom pattern and timeline.
This case illustrates why an environmental and displacement history must include country of origin and prior water source history, not just current exposures.
Source: WHO Guidelines for drinking-water quality. 4th ed. 2017.
Ellis
Ellis is a 48-year-old farmer in a rural region of Washington state who presents with worsening cough, fatigue, and intermittent loose stools over three months. His region experienced severe drought earlier this year followed by six weeks of regional wildfire smoke. His private well depth has dropped significantly, and he reports the water has a different taste than usual.
Which framing best reflects planetary health reasoning?
Wildfire smoke drives respiratory and cardiovascular effects: cough and fatigue. A private well dropping significantly during drought raises concern for chemical contamination from deeper bedrock, consistent with the changed water taste and a plausible explanation for the gastrointestinal symptoms. Neither exposure alone adequately explains all three symptoms.
- The first option correctly identifies the chemical contamination mechanism but incorrectly treats the cough and fatigue as coincidental.
- The second option incorrectly attributes gastrointestinal symptoms to smoke-related motility changes, which is not a well-supported clinical mechanism.
- The third option uses a real clinical fact—arsenic can cause airway irritation at high concentrations—but misattributes the cough in a way that ignores the more straightforward smoke exposure.
Planetary health reasoning requires holding both exposures simultaneously and recognizing their distinct clinical contributions.
Sources:
- Waterborne Diseases That Are Sensitive to Climate Variability and Climate Change. N Engl J Med. 2023;389:2175.
- WHO Guidelines for drinking-water quality. 4th ed. 2017.
Do you want a conclusion statement? Maybe considerations for students as they embark into clinical settings. Something like this line, “Planetary health reasoning requires holding both exposures simultaneously and recognizing their distinct clinical contributions.”
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Unless otherwise noted, images are from Adobe Stock.
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