“Legionella is widespread in water systems,” said Dr. Robert F. Breiman, one of the people who supervised the examination of Celebrity Cruises’ ship Horizon for the Centers for Disease Control and Prevention.
“If we cultured the cooling towers up there in New York City, we’d find Legionella in 50 percent. But the vast majority do not transmit disease. And we don’t have the answer why, and right now cannot predict.”
Breiman, who is the chief of the respiratory disease epidemiology section of the CDC in Atlanta, said that for that reason, testing water samples from all cruise ships for Legionella would still not detect where Legionnaires’ disease might originate.
Although the CDC has not completed its comparison interviews of Horizon passengers, of the infected as well as the healthy, Breiman’s associate, Dr. Martin F. Cetron, said that the sand used in the filters for the whirlpool tubs was “strongly implicated” as the source of transmission for the Legionella bacteria.
Bromine and chlorine are used as bactericides to treat water in whirlpool tubs, and Breiman said there was no reason to consider this treatment inadequate.
“But even the best bromination won’t be effective in a situation where the bacteria hide in sediment,” he said. Traces of Legionella bacteria were found in sediment in the sand filter.
The CDC has confirmed 11 cases of Legionnaires’ disease among the passengers of the Horizon; 24 other cases are suspected. One passenger died in what was the first cruise-ship outbreak of Legionnaires’ disease known to the government.
“Given that we’ve never seen anything like this before,” Breiman said, “we’re hoping it’s just an anomaly.”
When the Horizon went back to sea, the three whirlpools, all linked in one system, were shut down.
Al Wallack, a senior vice president of Celebrity Cruises, said that the filters had been removed and stored for any future study. Cetron said Celebrity had not been asked to shut the whirlpools permanently, but both the line and the government want to keep them out of service until more is known about the problem.
As for requiring that all ships’ water systems be flushed with a chlorine solution 25 times the usual strength, the method by which the Horizon was cleansed so it could re-enter service on July 31, Breiman said: “It’s not easy to get rid of the bugs. You have to keep doing it over and over. It’s very corrosive to plumbing, and you do not want to do it routinely.”
Breiman said that his agency dealt with five to 10 outbreaks a year of Legionnaires’ disease, although it’s possible that smaller outbreaks are managed by local health departments. The most frequent source is a building’s cooling tower, also known as an “evaporative condenser,” but he said that considering his estimate that 50 percent of these might contain the bacteria, the rate of disease transmission was infinitesimal.
The annual total of cases of Legionnaires’ disease in the United States is estimated at 25,000, some involving mild symptoms. The disease is treatable with antibiotics, but the fatality rate in an outbreak can be as high as 15 percent.
Legionella thrives in warm water, not above 125 degrees. Water at swimming pool temperature, 80 to 88 degrees, is too cool. Breiman said that most cruise ships store hot water for showers at 140 degrees, which kills the bacteria. Whirlpool or hot tub temperature, usually 98 to 103 degrees, “could not be better” for growth of the bacteria, he said.
“It’s a place where technology and disease trip over each other. The water is comfortable for you, it’s comfortable for the bacteria.” In addition, he said, the water contains enough organic material, particularly amoebas, for the bacteria to hide in.
Transmission is usually by inhalation, breathing an aerosol-a suspension of particles in the air, Breiman said. This is one of the things people like about whirlpools-the spray around the face.
Cetron said that in the fall the CDC will hold a conference of public health officials, Legionella experts and representatives from the spa and cruise industries to look at the problem. After that, the CDC will issue recommendations that will apply to resorts with whirlpools as well as to cruise ships.
One issue to be discussed, Breiman said, is whether filters should be easily replaceable, which is not the case now.
“Perhaps they should be designed as a removable unit, like an auto air filter,” he said.
Even if the Horizon outbreak was an anomaly, the case will probably have an impact on the cruise sanitation program of the CDC. Its current inspection program has focused on storage and delivery of things people ingest-water and food-to prevent diarrhea, the most common scourge of cruising. If Legionella transmission becomes a problem again, the inspection program will end up being involved, Breiman said.
The Vessel Sanitation Program now involves two unannounced inspections a year for every ship that sails from U.S. ports regularly for more than six months a year.
The vessels are charged per inspection on the basis of gross tonnage: $799 for small ships, $6,388 for the largest.
A passing grade is 86, and the government has the right to recommend that a cruise be canceled if conditions are hazardous, particularly if they involve the drinking water. A score of less than 86 does not mean cancellation. The summary report of June 17 showed that seven of 79 ships scored lower than 86.
The Horizon’s score for an inspection it underwent on Feb. 4 was 94. The chief of the sanitation program, Don W. Turner, said that Celebrity Cruises had had “a good track record” on inspections.
Turner said that until the recent incident involving the Horizon, no cruise ship had been prevented from sailing during his six years in the inspection program.
In a case like the Horizon’s, in which a state health department reports an outbreak, inspectors go to the ship immediately, along with epidemiologists from the CDC. Blood and stool samples are taken from both the ill and the healthy.
Breiman said he considered the whirlpool tubs to be suspect when he first saw them, but dozens of possibilities had to be tested.
The sanitation program issues two types of public reports, which are available together on request. The most recent scores for all ships visiting the United States, along with the date of inspection, appear on the Summary of Sanitation Inspections, a single card known as the “green sheet.” Travel agents can be expected to have copies.
A prospective passenger may also request the results of the latest inspection of a vessel. A document of several pages, it itemizes the score, gives the inspectors’ descriptions and a response by the cruise line concerning what it did to correct any problems.
Requests for a copy of the summary green sheet or the inspection report of a vessel should be addressed to: Chief, Vessel Sanitation Program, 1015 North American Way, Room 107, Miami, Fla. 33132.
