10 exam-style questions with answers and explanations, straight from our 1,030-question bank. Tap an answer to check yourself. When you're ready, take the scored version in the free practice test.
The CMI exam has 100 questions and runs 3 hours.
These 10 free CMI questions are organized by exam domain, so you can see how each part of the Council-certified Microbial Investigator blueprint is tested. Reveal the answer and explanation under each question.
After a sewage cleanup, an airborne-dust sample yields few culturable Gram-negative bacteria but substantial endotoxin activity by the Limulus amebocyte lysate assay. Laboratory quality controls are acceptable. How can these findings coexist?
Correct answer: D - Outer-membrane fragments can retain endotoxin after the Gram-negative bacterial cells have died.
A tape lift from the paper facing of gypsum board is examined to distinguish growth on the board from deposited airborne spores. Which microscopic finding provides the strongest evidence of growth at that surface?
Correct answer: C - An interwoven hyphal network anchored to the paper, with attached conidiophores.
After a hotel conference, clinicians confirm pneumonia in several older attendees. Others develop a short-lived febrile illness without pneumonia. Illness is associated with time beside an indoor whirlpool, not with drinking hotel tap water or eating catered meals. Which exposure should lead the environmental investigation?
Correct answer: D - Legionella exposure through inhalation of aerosols generated by the whirlpool.
While planning removal of mold-contaminated ceiling tiles in a mixed-use clinic, the team reviews who could be exposed. Which person raises the greatest concern for invasive aspergillosis, rather than an allergic response?
Correct answer: D - An adult receiving immunosuppressive treatment after a stem cell transplant.
A pinless moisture meter repeatedly flags narrow bands in an otherwise unstained gypsum wall. The bands align with metal studs, while readings midway between studs are low. Before recommending wall removal, the investigator should:
Correct answer: A - Check the suspect gypsum with a pin-type meter, keeping the probes clear of metal framing.
A manager reports that a water-damaged room is dry because electric heaters reduced its relative humidity from 68% to 41%. Over the same period, the recorded humidity ratio remained 9 g of water/kg of dry air. No final material-moisture readings were taken. How should this claim be evaluated?
Correct answer: B - The relative-humidity change can be explained by warming; material dryness remains unverified.
Comparable spore-trap samples collected during normal office use show 600 total spores/m³ indoors and 2,800 outdoors. Aspergillus/Penicillium-type spores dominate indoors; basidiospores dominate outdoors. An exterior wall behind a filing cabinet remains damp. What does the lower indoor total mean for the investigation?
Correct answer: C - It does not exclude an indoor source; the damp wall warrants targeted investigation.
A spore-trap cassette operated at a verified 15 L/min for 10 minutes. The analyst observed 30 spores while examining 25% of its deposit and reports an estimated whole-deposit count of 120 spores. The sample is valid. Which result uses the laboratory count correctly and preserves the meaning of this microscopic method?
Correct answer: B - 800 spores/m³; the method does not distinguish viable from nonviable spores.
Eight hours after a potable-water supply line breaks, a restorer finds wet paper-faced gypsum board with intact seams, no swelling, and no visible growth. The leak is repaired. The cavity is accessible, contains no wet insulation, and can be dried promptly. Which disposition best fits these findings?
Correct answer: B - Retain the board while actively drying and verifying dryness of the board and cavity.
From outside a below-grade utility vault at sea level, an investigator sees a coworker collapse. A calibrated monitor lowered into the vault reads 17.8% oxygen. The investigator has an air-purifying respirator with P100 filters but no supplied-air equipment or rescue training. The immediate response is to:
Correct answer: A - Remain outside, summon the designated confined-space rescue service, and prevent unprotected entry.
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