Environmental Engineering Reference
In-Depth Information
in water and wastewater treatment. On the other hand, disinfection combined
with secondary wastewater treatment may be sufficient to remove
Cyclospora
sp.
83
At present, there is the tendency to infer that inactivation steps effective
for containment of
Cryptosporidium
spp. ought to prevail with
Cyclospora
sp.
Incidence of cyclosporiasis in the United States up to the present is rare, and,
when suspected, is often without the presence of the tell-tale oocysts.
Legionnaires' disease is caused by
Legionella pneumophila
. Another form
is Pontiac fever, which typically has a shorter incubation period and results
in mild, influenzalike symptoms. The organism has been readily isolated from
surface waters and adjacent soils. Other sources are cooling towers and evapora-
tive condensers, hospital hot-water systems, whirlpools, showerheads, domestic
hot-water tanks, hot- and cold-water distribution systems, humidifiers, and open
water-storage tanks. The organism is primarily spread by aerosols and, to a much
lesser extent, water ingestion. It is a major problem in hospitals. Person-to-person
spread has not been documented.
84
A water temperature of 68
◦
to 114
◦
F(20
◦
to
45
◦
C) or 104
◦
to 122
◦
F(40
◦
to 50
◦
C)
85
appears to be most favorable for organism
survival. The critical temperature is believed to be 97
◦
F(36
◦
C). The organism
has been found in hot-water tanks maintained at 86
◦
to 129
◦
F(30
◦
to 54
◦
C)
but not at 160
◦
to 172
◦
F(71
◦
to 77
◦
C).
86
The FDA recommends a minimum
temperature of 166
◦
F(75
◦
C).
Suggested
Legionella
control measures include 1 to 2 ppm free residual
chlorine at water outlets, including daily testing; maintenance of continuous
chlorination and hot water temperature; annual cleaning and disinfection of the
cold-water system.
87
,
88
Consensus data suggests that 140
◦
F(60
◦
C) is the mini-
mal temperature for thermal disinfection of hot water plumbing systems and that
this temperature should be used in flushing outlets, faucets, and shower heads
for a period in excess of 30 minutes and maintained to prevent reestablishment
of L.
pneumophila
.
89
It should be noted that scalding is a potential hazard at
the recommended thermal inactivation temperature. It has been suggested that 4
to 6 mg/l residual chlorine, maintained in the facility for 6 hours, is sufficient
for disinfection, however, this level of disinfectant is difficult to maintain in hot
water and may cause problems with patients having transplant surgery.
90
In view
of the different findings, laboratory monitoring of the water in the distribution
system for
L. pneumophila
is also suggested.
Control and Prevention of Waterborne Diseases
Many health departments, particularly on a local level, are placing greater empha-
sis on water quality and food protection at food-processing establishments, cater-
ing places, schools, restaurants, institutions, and the home and on the training
of food management and staff personnel. An educated and observant public, a
systematic inspection program with established management responsibility, cou-
pled with a selective water- and food-quality laboratory surveillance system and
program evaluation, can help greatly in making health department food protec-
tion programs more effective. It is necessary to remain continually alert because
