A fly in your soup on a cruise ship? This is not taken lightly by the Centers for Disease Control.

The CDC inspects the hundreds of cruise ships that enter U.S. ports as part of its Vessel Sanitation Program, checking the ventilation and drinking water systems, looking for proper food preparation and storage, and inspecting the sanitation of common areas, dining rooms, swimming pools and medical facilities.

Based on their reports, the inspectors seem fastidious. They count flies. Examples of infractions in reports include a housefly noted on a bowl of pears, six flies in a pastry preparation area, a mosquito on the bulkhead behind an outdoor grill, and a fruit fly in an oatmeal station.

They note when they find coffee grounds under the coffee machine, mold on an ice bin, a broken salad washer, a pan of lasagna with no discard date, under-chilled yogurt, a clogged drain, a leaky pipe.

The cruise ships are scored on a 100-point scale; points are deducted from the score when there is a pattern of similar violations or when there is a single, significant violation. A score of 85 or below is considered not satisfactory.

These are the cleanest cruise ships -- those that scored 99-100 in the most recent inspections. Read on to see the ships that failed.

Photo: Yevgen Belich / Shutterstock