In recent years, an intestinal parasite known as cryptosporidium has infected visitors at dozens of public pools and water parks around the world, causing epidemics of diarrhea and sometimes killing people with weakened immune systems. A 1996 outbreak at a California water park was responsible for an estimated 3,000 cases of illness.

Part of the reason for such events is that the single-celled parasites form microscopic egglike bodies called oocysts with shells that are highly resistant to chlorine and other chemicals. A new study suggests that when a child with a leaky diaper contaminates a pool with cryptosporidium, the levels of chlorine currently recommended to deal with such accidents aren't sufficient to kill the organism.

Researchers at the U.S. Department of Agriculture and the federal Centers for Disease Control and Prevention (CDC) first tested oocysts' sensitivity to various chlorine concentrations in clean water. Then they simulated a swimming pool accident (such as might occur at a water park or "kiddie" pool) by mixing oocysts and fecal material into aquarium water, and repeated the chlorine tests under those conditions.

Chlorine's ability to kill microorganisms depends on the concentration of the chemical, the temperature and the duration of exposure. The normal recommended concentration of chlorine in pools is about 2 parts per million (ppm); in response to an episode of contamination, guidelines call for increasing the concentration to 10 ppm. But when the researchers tested these levels in fecally contaminated water, the cryptosporidium oocysts remained infectious--even after continuous exposure to the higher concentration of chlorine for 48 hours.

The authors recommended engineering and policy changes at public pools, including improved filtration, separate plumbing and filters for "kiddie" pools and more aggressive responses to accidental contamination. They recommend that anyone with diarrhea should stay out of the pool during the illness and for several days afterward. They also said parents should teach children not to swallow pool water and should require pre-swim showers, regular diaper changes, the use of swim diapers and frequent bathroom breaks.

The study was published in the July-August issue of Emerging Infectious Diseases, a CDC journal.

--Susan Okie


A recent study has found another example of the health gap between blacks and whites, this time in the area of dental care.

A study published last spring in the Journal of Public Health Dentistry by researchers at the University of Michigan has found that while African Americans and whites have similar dental care habits, African Americans see a dentist less often for routine care.

David L. Ronis, a researcher at the University of Michigan School of Nursing and the Veterans Affairs Medical Center in Ann Arbor, surveyed 384 African Americans and 358 whites living in the Detroit area who were over 18 years old. Ronis found that 13 percent of African Americans had never seen a dentist for routine care, compared with only 1 percent of whites.

The chief reason cited was lack of money or dental insurance.

Ronis and his colleagues also found that blacks in the study tended to have lower family incomes and were more likely to be enrolled in Medicaid. Researchers found that 37 percent of African Americans and 16 percent of whites reported that their families earned less than $20,000 annually. In addition, 13 percent of blacks were dependent on Medicaid for dental coverage, compared to 2 percent of whites. Some dentists refuse to treat Medicaid patients, citing low reimbursement rates, researchers noted.

When it comes to brushing and flossing habits, few differences were reported. More than 95 percent of both groups said they brushed their teeth every day, but whites were more likely to floss completely. Sixty-four percent of whites said they flossed all their teeth, compared with 47 percent of African Americans.

The study was funded by the National Institute of Dental and Craniofacial Research, a part of the National Institutes of Health.

--Sandra G. Boodman


Television newscasters do indeed look different from most people, a Japanese study confirms.

They blink more.

While the increased blinking is "a possible reaction to reading the news under stressful studio conditions," researchers noted, it "may be distractive to the viewing audience."

Researchers videotaped 24 Japanese newscasters, 12 men and 12 women, and calculated the average and maximum intervals between their eye blinks. For comparison, they also analyzed the blinking patterns of 64 volunteers under relaxed conditions.

The newscasters blinked almost once a second, on average, compared with once every four seconds for the relaxed volunteers. The maximum interval between blinks by the newscasters--2.3 seconds--was shorter than the average interval between blinks by the comparison group. One newscaster blinked 176 times per minute.

The finding surprised researchers, because previous studies had shown that people blink less than usual when they read or use video display terminals. Two possible factors, they said, are that "newscasters are presumably under pressure not to make errors and the environment in the TV studios is bright and dry."

Normal blinking is an involuntary action that protects the surface of the eye. But frequent blinking is often thought to indicate nervousness.

"When the audience feels uneasiness or nervousness while watching news broadcasts, it might not be due to the bad news itself, but to the high and irregular frequency of the newscasters' blink rates," researchers said.

The study was conducted by a team of ophthalmologists at Tokyo Dental College and Keio University School of Medicine in Tokyo. They reported their findings last month in a letter to The Lancet, a medical journal.

--Don Colburn