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Single Cryptosporidium

Ben and Gerri had been saving for years for their dream vacation cruise to Bermuda on the luxury ship Endemic.   They had a great time eating all day at open buffet tables, swimming in the deck pool and touring islands. Ben even took his first jacuzzi.

However, by the last few days of the trip, they were both feeling pretty poorly– tired, coughing, fever.  A few weeks later, Ben, Gerri & 16 other passengers were hospitalized with Legionnaires’ disease. There were 30 other suspected cases, and one person died.

As Director of Public Health for the cruiseline, you call the Center for Disease Control (CDC) to help investigate.


INSTRUCTIONS: We have developed a series of questions for you to answer as you go through this case study. Download and print a copy of the WORKSHEET.


Background Information:



Looking for the pathogen:

The ship was immediately quarantined.   Scientists from the Center for Disease Control (CDC) took samples from across the ship (see sample locations below).   As a consultant for the cruise ship, you need to know: What caused the disease? Where is it hiding?  How will you find it? And how can you get rid of it?

Looking for Legionella

Water samples were brought to your lab where you observed them under a fluorescence microscope using the Direct Fluorescence Antibody Assay, using a tagged antibody specific to Legionella.

You viewed a control sample (from a pure culture of Legionella) and water samples from 3 locations across the ship. Here’s what you saw:

Cafe Sink Hot Tub Room Sink

You ask the CDC to go back and swab the surfaces instead of just taking water samples. Again, after treating the samples with a tagged antibody specific to Legionella, here is what you saw:

LegionellaControl Cafe Sink Hot Tub Room Sink

Your Experiments

You know the crew of the Endemic is supposed to routinely rinsing their water system with chlorine, but you see a BIG problem here. You need to come up with a better treatment program.

Back at your lab, you set up a prototype water system. The system consists of a series of square PVC pipes with 24 removable pieces (the gray boxes below) on one side.   Water flows in one end and out the other. You can control the flow rate, and the content of the water that flows through each experimental pipe.

Each different treatment starts out with water from the storage tank of the cruise ship Endemic and a sub-sample of the Legionella biofilm. In each case the flow rate is 0.2 m/s and the temperature is held constant T= 38°C (unless otherwise noted). These systems are maintained for 2 weeks to give the biofilm a chance to develop.

You research some different ways to kill bacteria, then begin your treatment conditions on Day 0.

Control Water from ship’s hold, no treatment
Chlorine Final concentration of 1 ppm (part per million; current treatment )
HEAT + Chlorine Super-heat to 60C for 5 minutes, followed by 1 ppm chlorine
UV Radiation 5 W s /m2
Ozonation Final concentration of 1 ppm ozone
Ozonation with Chlorine Final concentration of 1 ppm ozone with 1 ppm chlorine

At Day 0, 10 and 25, you remove a piece from each treatment pipe and analyze it using the DFA assay.  


Treatment Results

The results of all your treatments are given below.  As you look at each result, use the micrographs to determine whether the treatment was successful in controlling the growth of the biofilm or not.  A no-treatment control is shown for comparison.

DAY 10
DAY 25



It is time to make your recommendation!

Review all your results and pull the information together to make a thoughtful, logical recommendation.  What treatment is best for treating the water system on the Endemic?



Your answers should be thoughtful and well-organized, and it must incorporate the results you obtained in this case study. That is, use the information from your results and in the references to support your final conclusion.