Raising the Standard on Safe Drinking Water

In the spring of 1993, thousands of Milwaukee residents were suffering from watery diarrhea and intestinal cramps. More than 400,000 people were estimated to have been infected, causing massive absenteeism among school children, health workers and other professions. Bill MacKenzie, an EIS officer assigned to the Wisconsin Division of Health, recalls getting a call from the city's epidemiologist requesting help with isolating the cause of the outbreak.

"It was clear that they needed assistance," says MacKenzie, who along with four colleagues at the division, headed to the city offices to meet with the mayor and city health officials. "We knew that when large numbers of people are ill with diarrhea in a large geographic area, one cause has to be from a product that is widely distributed," MacKenzie says.

It didn't take them long to zero in on a possible cause – the city's drinking water – and particularly, drinking water from the southernmost of Milwaukee's two water treatment plants. At the time, Milwaukee residents and the rest of the country trusted that their drinking water was safe, and some considered it to be " sterile," MacKenzie says.

"The first bit of information we got was that the southern water treatment plant had increases in turbidity, which is a measure of how well the water is filtered. What we didn't know at the time was that those increases had been unprecedented compared to the prior 10 years. They were really off the chart for that water department."

The second clue came later that day, when laboratories around the city confirmed seven cases of Cryptosporidium, a waterborne, chlorine-resistant pathogen that causes diarrhea. "It was known among public health officials that drinking water could be associated with a Cryptosporidium infection," MacKenzie notes. Cryptosporidiosis was first recognized in humans with weak immune systems in 1976 and later was proven to also affect people with normal immune systems. In fact, MacKenzie recalls that a number of Milwaukee patients who had AIDS or otherwise compromised immune systems were not able to recover from their cryptosporidiosis and died with the infection.

With the initial findings in hand, Milwaukee officials immediately issued a boil-water advisory to keep the infection from spreading while MacKenzie and his public health colleagues continued their investigation. They surveyed nursing homes throughout the region for signs of the infection and found a much higher prevalence of diarrhea among homes in southern Milwaukee with the exception of one, which used a private well for its water supply. Then, they conducted massive telephone surveys with residents, which showed a much higher infection rate for residents living or working near the southern water treatment plant. Laboratory examination of specimens ruled out other known pathogens as the cause. The investigative team even melted large, 60-gallon blocks of ice made during the peak period of the outbreak from a nearby ice maker to prove that the water contained Cryptosporidium. According to MacKenzie, the need to gather "overwhelming" evidence on the outbreak's cause was necessary.

"When you're faced with a large-scale outbreak, people are always going to question whether or not the cause is primarily due to the water," says MacKenzie. "Our investigation helped the water industry officials in the United States realize they had a problem and they needed to do something about it. It helped public officials understand that they needed to spend more resources to maintain safe water supplies. The outbreak also re-educated everyone, including doctors, that Cryptosporidium could cause disease in people with normal immune systems."

The documentation on the Milwaukee outbreak helped put Cryptosporidium and the need for better drinking water treatment "on the radar screen for water engineers, politicians and regulators," adds MacKenzie. To their credit, residents in Milwaukee complied with the advisory to boil water, which effectively killed the pathogen.

MacKenzie says the quality of public water systems has improved significantly since 1993, but there are still areas for improvement. Water treatment plants in larger cities with access to public capital have made improvements, including using advanced techniques to monitor water quality and better water filtering techniques to make the water safer. However, smaller cities without resources still struggle to maintain their water supplies adequately.

Concerns about Cryptosporidium-contaminated drinking water extends beyond our borders. Two years ago, while preparing for the Olympics, Sydney, Australia, had a Cryptosporidium scare. When using a new testing method the pathogen was found in Sydney drinking water. Those tests turned out to be false, but nevertheless caused the city to issue three boil-water advisories.

And, Cryptosporidium continues to cause problems in recreational waters, such as swimming pools, lakes and rivers, which likely are the largest source of cases, according to MacKenzie. Since these cases occur predominantly in children, "CDC has been working on communicating the risks of contaminated recreational water such as swimming pools to parents for several years now."

Following EIS, MacKenzie went on to work at CDC for five years until 1998. First, he trained state-based EIS officers in field epidemiology at CDC's Epidemiology Program Office. Later, he worked at the parasitic disease program, helping the EPA and CDC in their efforts to come up with a national estimate for waterborne diseases. In 1998, he left CDC to travel to Kosovo, where he assisted with the rebuilding of the country's public health system. He currently heads up outbreak investigations and FoodNet (a CDC-supported research program for foodborne diseases) for the Georgia Division of Public Health. He continues to strongly support the EIS.

"The EIS is a wonderful training program to provide bright, young people an opportunity to work in an applied setting and use their knowledge to improve the health of the population," he says. "It also works well for state and local health departments and CDC to have these bright minds thinking in new and different ways to keep the wheels of public health turning and to keep us from stagnating.

"My EIS experiences in Milwaukee and other areas of the world certainly have made me a better epidemiologist and physician. It's helped me understand the broader context of how public health affects society, not just one patient at a time."