Cryptosporidium Overview and Milwaukee Outbreak

Cryptosporidium

• Cryptosporidium was first isolated in 1907, but the first human cases were reported in 1976.
• Type 1 is now called Cryptosporidium hominis and linked to human reservoirs.
• Type 2 is now called Cryptosporidium parvum and linked to bovine and human reservoirs.
• Cryptosporidium felis, C. meleagridis, and a new cervine (deer) genotype are uncommon human infection causes but are more common in HIV-infected patients.
• The protozoan is found in fish, amphibians, reptiles (snakes, lizards, tortoises), wild and domesticated birds (chickens, turkeys, ducks, canaries, cockatiels), and mammals (rodents, cats, dogs, sheep, goats, pigs, deer, cows, and humans).

1993 Milwaukee Outbreak

• In March/April 1993, Milwaukee, Wisconsin experienced a cryptosporidiosis outbreak affecting 403,000 people.
• Two water treatment plants serving 800,000 residents and 10 other municipalities were implicated.
• The South plant showed increasing turbidity, starting March 21st, reaching higher levels from March 23rd to April 5th.
• A boil water order was issued on April 7th.
• The plant temporarily closed on April 9th.

Outbreak Impacts

• A medical record audit during and after the outbreak showed 88% of infected individuals did not seek medical care, 11% sought patient medical care, and 1% were hospitalized (average stay: 8 days).
• The estimated cost of the outbreak was approximately $96.2 million, with 67% attributable to lost productivity.
• A 2-year follow-up study revealed 54 death records indicating cryptosporidiosis as a contributing or underlying cause of death. 85% of these cases were linked to AIDS.

Transmission

• Transmission occurs via the fecal-oral route, contaminated drinking or recreational water, and food.
• Close contact with infected humans or other species (e.g., petting zoos) is also a potential transmission pathway.
• Environmental contamination is common worldwide. A study showed oocysts in 27% of drinking water samples from 66 inspected treatment plants.
• Implicated food sources include raw vegetables (like basil and cilantro), fresh-pressed apple cider, chicken salad, and shellfish.

Infection Process

• The incubation period is 2-14 days, averaging 7 days.
• Children and older adults have a shorter incubation period (around 5 days).
• The round, thick-walled oocyst is 4-6 µm in diameter.
• After ingestion, enzymes and bile salts trigger excystation, releasing four sporozoites that enter intestinal cells.
• Each sporozoite matures and divides asexually, producing 4-8 merozoites.
• Merozoites either reinvade intestinal cells or begin sexual maturation to a zygote and ultimately a sporulated oocyst.
• Approximately one in five oocysts are thin-walled to re-infect the host.
• Remaining thick-walled oocysts are passed in feces to the environment.
• The mechanism of disease is unknown, but as few as 30 oocysts can cause infection, with the average infectious dose around 130 oocysts.
• Oocysts are immediately infective after excretion.

Symptoms

• Illness duration is 2-14 days for immunocompetent individuals; a chronic stage is common in immunocompromised individuals, though the range is 1-53 days.
• The major symptom is diarrhea (average of 12 stools per day, with values < 25 L/day possible).
• Oocyst excretion can persist for months after diarrhea stops.
• Other possible symptoms include nausea, fever, vomiting, and cramping.
• C. hominis infections might also present with joint pain, eye pain, recurrent headaches, and fatigue.

Pathology

• The organism primarily affects the intestines and appendix in immunocompetent hosts.
• In immunocompromised patients, the organism can be found in the GI tract, the hepato-biliary system, and the respiratory tract.
• Illness is typically self-limiting in healthy individuals treated with oral rehydration and anti-diarrheal drugs.
• Immunocompromised individuals with CD4+ cell counts >200/mm³ usually experience a resolvable acute illness.
• Those with CD4+ cell counts <100/mm³ are prone to chronic illness, potentially life-long, and may have extra-intestinal disease.
• CD4+ cell counts <50/mm³ individuals might experience a fulminating, life-threatening form of cryptosporidiosis.
• In the acute phase, up to 10¹⁰ oocysts may be released daily. Excretion is intermittent, and three independent stool samples collected on different days reduce false-negative results.

Control

• Environmental control involves improved filtration, ozonation, and ultraviolet (UV) light.
• Current chemotherapy is deemed suboptimal, though paramomycin therapy for a week and HAART (Highly Active Antiretroviral Therapy) in AIDS patients are options based on severity and immune system conditions.
• Oocysts are resistant to chlorine, Cidex (gluteraldehyde), and Lysol (ortho-phenylphenol).
• Water facilities meeting regulatory requirements may not adequately protect immunocompromised individuals.
• Recommendations for those in these populations include using reverse osmosis systems, boiling water for one minute, and using submicron filters for drinking water.

Explore the details of Cryptosporidium, a protozoan parasite linked to various animal reservoirs and human infections. This quiz also covers the significant 1993 outbreak in Milwaukee, which affected over 400,000 individuals due to contaminated water sources.