CHAPTER 14 The Massive Waterborne Outbreak ofCryptosporidium Infections, Milwaukee

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CHAPTER 14 The Massive Waterborne
Outbreak ofCryptosporidium Infections,
Milwaukee, Wisconsin, 1993

Jeffrey P. Davis, MD
Wisconsin, 1993

INTRODUCTION: APRIL 5, 1993
On Monday morning, April 5, Dr. Gerald Sedmak, a virologist with the City of
Milwaukee Health Department (MHD), received calls from individual citizens
complaining of gastrointestinal illnesses. Gerry told other MHD staff about
these complaints, and in turn, these staff members began an effort to see
whether there was an unusual number of individuals with similar
gastrointestinal illness—indeed, there were. Kathy Blair, a registered nurse

and epidemiologist with the MHD, received calls from the South Milwaukee
Health Department, other local agencies, and private citizens regarding
widespread occupational and school absenteeism related to diarrheal illness.
Gerry, Kathy, and their colleagues could not have known at that time that
these were the initial reports of what would unfold as a historically large and
unprecedented waterborne outbreak in the United States. Many pharmacies
on the south side of Milwaukee had or were nearly sold out of antimotility
medications (medication to slow down or stop diarrhea). Additionally, many
health care providers were ill and unable to work. Concomitantly, Dr. Steve
Gradus, director of the MHD Bureau of Laboratories, and his colleague,
Dr.Ajaib Singh, conducted telephone surveys of hospital emergency rooms
and laboratories. They learned of an extreme number of weekend visits for
diarrhea-related illnesses to emergency departments and increased numbers
of requisitions for bacterial culture of stool specimens. The St. Luke’s Hospital
microbiology laboratory exhausted its supply of media used to isolate enteric
bacterial pathogens. Based on this information, MHD officials suspected that
the outbreak was predominantly affecting the southern part of Milwaukee
and included other municipalities in southern Milwaukee County. Initial
newspaper and other media reports circulating on April 5 focused on the
unusual number of diarrhea illnesses, the unknown etiology of the illness,
and the shortage of antidiarrhea medications. Media interest intensified
rapidly.
Kathy called Jim Kazmierczak, DVM, an epidemiologist and colleague in the
Bureau of Public Health (BPH), Wisconsin Division of Health (DOH; now
named the Wisconsin Division of Public Health), notified him of these events,
and inquired whether DOH staff were aware of an unusual occurrence of
similar illnesses elsewhere in the state. Up to then we had not been told of
similar illnesses elsewhere.
During my initial conversations with Kathy and Jim that morning, we
discussed the potential of any one of several etiologic agents to be
associated with these events and the need for good laboratory data and
illness characterization. Although the agent was not yet known, my initial
impression was the illness must be considered to be water-borne until proven
otherwise because of the magnitude and widespread occurrence of diarrhea

illness. Concomitantly, Drs. Gradus and Singh discovered that most hospital
microbiology laboratory staff members were not conducting virus culture of
stool specimens and that tests for ova and parasites were infrequently
ordered. Accordingly, infection control practitioners were selected to
facilitate collection of stool specimens for virus culture at the MHD from the
next 10 patients presenting at their facilities with diarrhea illnesses.
Although the agent was not yet known, my initial impression was the illness
must be considered to be waterborne until proven otherwise because of the
magnitude and widespread occurrence of diarrhea illness.
Later, we discussed the MHD plan to widely distribute stool kits for virus
testing to clinics to test individuals with acute diarrhea illnesses and the
results to date of testing for bacterial enteric pathogens at St. Luke’s
Hospital. We sensed that this was a really big outbreak when we learned that
from this one hospital on one weekend about 200 stool specimens were
obtained for bacterial culture, and we were confronted with a really big clue
when we learned that, despite this high volume of testing, all cultures were
negative to date for bacterial enteric pathogens. I suggested testing stool
specimens already known to be negative for bacterial enteric pathogens and
still remaining at the St. Luke’s laboratory for parasitic and protozoan
infections at the MHD laboratory. The MHD laboratory was one of two public
health laboratories in Wisconsin. The emerging scope and breadth of this
outbreak diminished the likelihood that this was a viral illness, and it was
important to consider protozoan infections, as they could be associated with
large community outbreaks.
Steve arranged for this testing and also requested that microbiology
laboratory supervisors begin aggressively testing diarrhea stool specimens
for protozoan infections, with specific emphasis on testing
for Cryptosporidium. Steve also planned to review water treatment records
that would be available from the City of Milwaukee Water Works (MWW), the
municipal water utility.
Because of the apparent magnitude of the outbreak and implications for
residents in multiple jurisdictions, I offered the onsite assistance of DOH staff

to join the MHD in the investigation. We would need Tuesday, April 6 to
structure a team and plan our activities in Milwaukee and would drive to
Milwaukee from Madison early on Wednesday, April 7. The offer of assistance
was accepted.

APRIL 6, 1993
On April 6, I spoke with Steve to discuss the findings of his review of the
MWW water treatment records. He described some initial resistance to
review the records and defense of the quality of Milwaukee’s water by the
MWW administrators, but he was able to review some recent water
treatment records. Generally, during recent weeks, there were increases in
coliform counts that were consistent with substantial rainfall at water intake
points; however, chlorine levels were high, and E. coli counts were within
Department of Natural Resources (DNR) recommendations after treatment.
Steve also noted spikes in treated water turbidity (one of many measures of
water quality) occurred in late March primarily at the South plant, one of the
two municipal water treatment facilities operated by the MWW. Turbidity is a
technical measure of particles suspended in water. Turbidity can be
measured in raw, untreated water and in finished, treated water. Steve was
impressed with peaks in turbidity values of treated water on successive days.
Turbidity is a technical measure of particles suspended in water.
While we were discussing these unusual turbidity test results, Steve recalled
the Carrollton, Georgia, outbreak of waterborne Cryptosporidium infections
involving an estimated 13,000 diarrhea illnesses—a lot of illness by any
measure.1 The Carrollton outbreak was associated with a filtered water
supply; however, the peak filtered water turbidity was less than 1
nephelometric turbidity unit (NTU). That was surprisingly low. The NTU values
in Milwaukee were considerably greater. Based on Steve’s preliminary
information, the potential that Cryptosporidium was the etiologic agent in the
Milwaukee outbreak seemed increasingly likely. I requested Steve to arrange
a meeting early on April 7 with the MWW directors and an opportunity for our
staff to review the water treatment records. This would be our first meeting
in Milwaukee after arriving on site.

Typically, notifiable enteric diseases are reported when an etiologic agent is
laboratory confirmed, although in Wisconsin outbreaks were to be reported
upon suspicion regardless of whether the etiology is known. Also, relatively
few individuals with true notifiable infections ever get tested, and diarrhea
without laboratory data is not reported by physicians. Thus, several strategic
surveillance activities were planned. I contacted Dr. Dennis Juranek, the chief
of the Parasitic Diseases Division in the National Center for Infectious
Diseases, the Centers for Disease Control and Prevention (CDC). Dennis had
extensive experience with waterborne diseases and had directed the CDC’s
investigation of the Carollton outbreak.1 We discussed the Carrollton
outbreak, and Dennis suggested examining illness occurrence in nursing
home populations, which were geographically fixed and not likely to obtain
their drinking water from other sources or sites.
Later that day Steve set up acid fast smears from three stool specimens
known to be bacterial culture negative. The test would determine whether
the patients were infected withCryptosporidium. The specimen staining
procedure required an overnight interval before the results would be known.

APRIL 7, 1993
While driving to Milwaukee early on April 7 with Mary Proctor, PhD, MPH, and
chief of the BPH Communicable Diseases Epidemiology Section, I discussed
our prospective and retrospective surveillance needs. We decided it would be
valuable to establish immediately a surveillance focus in two settings. Mary
would establish and maintain surveillance for diarrhea illness in nursing
homes and emergency departments throughout Milwaukee County and its
four contiguous counties.
Bill Mac Kenzie, MD, was the CDC Epidemic Intelligence Service (EIS) officer
assigned to the DOH who I supervised. Bill, Jim Kazmierczak, Mary and I from
the DOH, Steve and Kathy of the MHD, and Wisconsin DNR staff met with
MWW officials, and we were briefed on their water treatment methods and
distribution system. The DNR had purview over regulation of drinking water
utilities.

Drinking water for the City of Milwaukee (1993 population estimate of
630,000) and many of the other 18 municipalities in Milwaukee County was
supplied by two MWW treatment plants, one in the northern part of the city
(Linnwood Avenue Purification Plant, North Plant) and one in the southern
part of the city (Howard Avenue Purification Plant, South Plant). Each plant
had a submerged water intake grid in Lake Michigan about 1.25 (North) and
1.44 (South) miles offshore, respectively, where water entered an enormous
tunnel and flowed by gravity through additional tunnels until it reached
stations to pump water to the respective plants. The North Plant was located
just offshore, but the South plant was located 3.5 miles inland from the Lake
Michigan south shore (Figure 14-1).
The North Plant was a strikingly beautiful structure situated on a prominence
projecting into Lake Michigan that was initially opened in the 1930s, and it
could be viewed from the hills overlooking Lake Michigan. I grew up in a
village along the north shore in Milwaukee County, passed by the treatment
plant many times, and truly appreciated the majesty of this municipal water
treatment facility. The same could not be said for the South Plant, built
during the 1960s. Nonetheless, both plants housed modern, large treatment
facilities.
Treatment capacities of each plant were sufficiently large to supply the entire
water district fully. Treated water needs in Milwaukee are great because of its
large population and industrial base, which included industries such as
brewing that required large volumes of pure water. Should an outage occur in
one plant, the distribution infrastructures from each plant were
interconnected so that either plant could supply the water needs for the City
of Milwaukee and its retail water customers elsewhere in Milwaukee County.
With both plants in simultaneous operation, the South Plant predominantly
supplies water to the southern portion of the district, and the North Plant
predominantly supplies the northern portion. Central Milwaukee was typically
supplied by both plants.
At the time of outbreak occurrence, water treatment in both plants followed
the same sequence: the intake of raw water, the addition of chlorine as a
disinfectant and polyaluminum chloride (PAC) as a coagulant to the raw

water followed by rapid mixing, mechanical flocculation to remove solid and
particulate material, sedimentation of the flocculent, and rapid filtration. The
South Plant had 8 filters, and the North Plant had 16, each of which was
enormous. After filtration, the water was pooled in a massive clear well at
each plant (35 million gallons at the South Plant) from which it was
distributed to customers (Figure 14-2). Parts of the water distribution
infrastructure were very old, including large pipes, and MWW staff members
were concerned that lead and copper could be leached if the pH of the water
was too low. To address this concern, the MWW changed coagulants in late
1992 from the venerable and time tested alum to PAC.

FIGURE 14-1 Location of the North and South
Milwaukee Water Works water treatment
plants, the water intakes for these plants,
the three rivers that flow through Milwaukee
County, and the breakfront located in the
Lake Michigan harbor.

FIGURE 14-2 Schematic of the water
treatment process at the South Milwaukee
Water Works water treatment plant in March
and April, 1993.

Testing treated water for a variety of water quality indices was required by
the DNR and the federal Environmental Protection Agency (EPA) and was
done three times each day at each plant before water was released from the
clear wells. Tests of water quality included bacteriologic (E. colitesting and
coliform counts), chemical (residual chlorine, residual fluoride, alkalinity, and
pH), and physical (color, threshold odor, raw water temperature, and
turbidity) tests. The treated water was then distributed from the clear wells.
Treated water leaving the plant was referred to as plant effluent. I do not
believe I have ever asked anyone whether they would like a nice tall glass of
cold plant effluent.
During March and April 1993, the turbidity of water treated at the South Plant
and distributed to customers increased with spikes to historically high values.
Early in March, there were no significant increases in finished water turbidity
despite turbidity spikes in raw water; however, on March 23, the turbidity of
South Plant treated water exceeded 0.4 NTU. This had not occurred in more

than 10 years. Furthermore, the peak daily turbidity on March 28 and March
30 reached 1.7 NTU, even though the dosages of PAC were adjusted. When
turbidity rises, the concern is that something dirty is getting into the system.
The goal is to get it to precipitate out or be filtered out before it gets into
someone’s nice tall glass of effluent. Chemists at the South Plant
aggressively tried to control the turbidity by changing the dosage of
coagulant, but PAC was not the coagulant they were used to using,
particularly under such extenuating circumstances. Plant staff resumed use
of alum instead of PAC on April 2, but a spike in finished water turbidity to 1.5
NTU occurred on April 5.2,3

FIGURE 14-3 Maximal Turbidity of Treated
Water in the Northern and Southern WaterTreatment Plants of the Milwaukee Water
Works from March 1 through April 28, 1993.

NTU denotes nephelometric turbidity units. From Mac Kenzie WR, Hoxie NJ,
Proctor ME, Gradus MS, Blair KA, Peterson DE, Kazmierczak JJ, Addiss DG, Fox
KR, Rose JB, Davis JP. A massive outbreak in Milwaukee of Cryptosporidium
infection transmitted through the public water supply. N Engl J
Med 1994;331:161–67.
There were substantial differences in daily comparisons of South plant and
North Plant finished water turbidity (Figure 14-3); the North Plant treated
water turbidity did not exceed 0.45 NTU. The MWW administrators, although
mindful that treated water turbidity at the South Plant was unusually high,
noted the turbidity results and other water quality measures were in
compliance with state and federal regulatory standards. Turbidity related
compliance was based on average results over one month. Bill Mac Kenzie
and Steve Gradus thought MWW administrators viewed turbidity as less
important than other measures of water quality, and more as a measure of
clarity. Notably, continually during February through April 1993, samples of
treated water for water quality testing obtained from both plants were
negative for coliforms. Coliforms are a group of related bacteria whose
presence in water may indicate contamination by disease causing
microorganisms. Thus, it became strikingly apparent that the likely focus of
the outbreak was the water treated in and distributed from the South Plant.
Using water quality indices, there were clear differences in finished water
quality between the North and South Plants during the same time interval.
Nonetheless, this did not exonerate treated water from the North Plant.
Later, on April 7, raw and treated water quality records for an interval that
exceeded 10 years were available from the MWW. I examined the turbidity
data and plotted the monthly peaks in finished water turbidity from each
plant for the past 10 years. Indeed, the initial spike in South Plant finished
water turbidity of greater than 0.4 NTU represented the first time in more
than 10 years that the finished water from this plant exceeded 0.4 NTU.
Thus, the three major spikes occurring during March 28 through April 5 were
truly historic peaks in turbidity.
After several internal planning meetings early in the afternoon, MHD
Commissioner Paul Nannis and I met with the press regarding our initial

impressions. I discussed the strong likelihood that this was a waterborne
outbreak and that the prime focus of our investigation was the South Plant,
but we would also pursue additional hypotheses. I noted that testing of stool
specimens for bacterial enteric pathogens was all negative; however, results
of testing these negative samples for a variety of other pathogens were
pending.
While I met the press, Jim Kazmierczak and Bill Mac Kenzie were meeting
with MHD staff when they received a call from Steve Gradus who reported
MHD Bureau of Laboratories staff foundCryptosporidium oocysts in the three
stool samples known to be bacterial enteric pathogen negative that he had
set up the day before. In addition, staff from the St. Luke’s Hospital
laboratory notified Steve that they had detected Cryptosporidium oocysts in
stools from 4 patients. These stools were obtained from 7 healthy adults who
resided in the Southern half of Milwaukee. Steve also received a report of a
case of Cryptosporidium infection in an older resident of West Allis in
southwest Milwaukee County. That laboratory diagnosis was made by an
astute microbiologist at West Allis Memorial Hospital who tested the stool
specimen for Cryptosporidium oocysts even though the test was not
specifically ordered. Steve, Bill, and Jim recognized the significance of these
laboratory findings. Given our findings and recalling those from the Carrollton outbreak that affected an estimated 13,000 people,1 these laboratory
results from only eight adult individuals were very significant.
After the press session, Paul and I were to meet with Milwaukee Mayor John
Norquist to discuss our findings and investigation plans. While walking to the
mayor’s office, I was met by Bill and Jim and was informed of the eight
laboratory-confirmed cases of Cryptosporidium infection. They
believed Cryptosporidium was a highly plausible etiology for this outbreak,
and I concurred. Bill raised the issue that a widespread boil-water advisory
involving all users of City of Milwaukee municipal water would be needed to
prevent additional cases.
The meeting with the mayor involved a substantial number of MDH, MWW,
DNR, mayor’s administration officials, and our DOH team. The water
treatment and quality data and state and federal water related regulations

were discussed in detail with the mayor. Based on preliminary findings and
illness characteristics, an outbreak of this nature that was so widespread
would be considered as waterborne unless proven otherwise. We discussed
the likelihood that this large waterborne outbreak was caused
by Cryptosporidium infection based on laboratory data that we had just
become aware of. We informed the mayor of our investigation plans to
consider all possible sources of these infections.
The discussion ultimately focused on what could and should be done to
control the outbreak. A variety of approaches were discussed, including
disinfection and a boil-water advisory.Cryptosporidium was a highly chlorineresistant protozoan, thus disinfection would not be effective. To be clear,
chlorine will kill Cryptosporidium; however, the concentration needed would
be great, and treating water with a concentration of chlorine that can quickly
kill Cryptosporidiumwould make the water unsafe to drink or bathe in for too
long of an interval and at great expense given the magnitude of the water
supply. The pros and cons of a boil-water advisory were considered.
Although Cryptosporidium oocysts were heat sensitive and inactivated with
boiling, the downside involved the need to boil all water treated in MWW
plants to be used for eating and drinking, the personal injury risks associated
with boiling water and with consuming recently boiled water, and the bump
in energy use that would be associated with a prolonged advisory. The
educational needs to conduct this activity effectively would be enormous.
Plus, all of these considerations were based on limited and newly available
information. Ultimately, the mayor focused his attention on a soft drink can
that I brought to the meeting and asked me, “Would you drink a glass of
water here, right now?” I replied, “No.” Mayor Norquist then stated, “That’s
it. We need to go public with what our suspicions are.”4 Clearly, if I would not
drink the water, he would not let Milwaukee residents and visitors drink it
unless it was safe to do so.
With no pun intended, this was a watershed moment. The mayor would
invoke a boil-water order, and his staff notified the media of a press
conference that evening. Precision was needed to provide clear instructions
to all users of the water. The implications of this massive boil-water advisory
were enormous. Municipal staff members would need to answer many

questions. That evening during the press conference, the mayor told all city
residents and all users of MWW water to boil their drinking water for 5
minutes and discard all ice.
Because of the need to obtain critical water samples to document any
presence of Cryptosporidiumin water from each of the implicated treatment
plants, systematic sample collections were planned for April 8, and the South
Plant would be closed for an undetermined interval beginning on April 9.
From April 8 throughout this undetermined interval, all drinking water in
Milwaukee would be supplied by the North Plant.
This was an enormous news story with national and international
implications. The local media gave this virtually unprecedented coverage.
The two major (and competing) Milwaukee newspapers collaborated in
publishing a special issue in Spanish. Plans for daily media updates were
announced. A half-page ad for an over-the-counter antimotility medication
appeared, but now that a boil-water order was invoked, what would be
needed to lift it? It was my responsibility to answer that question, but there
were so many questions to answer and avenues to explore to describe fully
the scope and all aspects of this outbreak, to generate and test hypotheses
regarding how it occurred and why it was so large, and to determine whether
measures were to be effective in controlling it.

THE OUTBREAK AND THE OUTBREAK
INVESTIGATION
This is what was known about Cryptosporidium before April, 1993:
We needed to learn quickly what was known about Cryptosporidium,
particularly regarding its associations with waterborne disease outbreaks. At
the time of this outbreak, relatively few public health officials had much
knowledge of this protozoan parasite and its associated illnesses, nor was it
well known as a pathogen by those charged with keeping local supplies of
drinking water safe.
Although initially detected in animals in 1907 and for years thought not to
affect humans,Cryptosporidium was first reported as a human pathogen in

separate case reports of enterocolitis in immune competent5–7 and
compromised8,9 patients. Cryptosporidium became a prominent pathogen
when it was recognized in 1981–1982 as an AIDS-defining illness and
opportunistic infection. The initial report in 1984 of a waterborne disease
outbreak of cryptosporidiosis was associated with an artesian well in San
Antonio, Texas. During 1986 to 1992, waterborneCryptosporidium infections
were associated with surface water exposure in New Mexico (1986), posttreatment contamination of drinking water in Aryshire, UK (1988), and
filtered water supplies in Carrollton, Georgia (surface, 1987), Swindon and
Oxfordshire, UK (1989), the Isle of Thanet, UK (1991), and most recently in
Jackson County, Oregon.10–14 The outbreak that was most similar to ours was
the one in Carrollton.

Early Logistics
It was rapidly apparent this outbreak investigation would require work w…

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