Overview of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 11

Resistance to Disinfection
The resistance to disinfection describes the likelihood that a pathogen will retain
infectivity following exposure to a disinfectant. The standard method of disin-
fection in the water industry has relied upon chemicals, particularly chlorine.
While highly effective for bacteria, viruses and protozoa display different levels of
resistance. Due to the robustness of some of these pathogens, alternative mecha-
nisms such as exposure to UV or ozone have been explored, and adopted, within
the water industry. The resistance to disinfection can be characterized in terms of
the percentage of organisms inactivated in a particular time, which can be stud-
ied experimentally.
In this chapter, and the WHO list, the resistance to disinfection is considered
low if 99% of organisms are inactivated in 1 min, moderate if 99% inactivation
takes 1-30min and high for times longer than 30min (for freely suspended
organisms, at conventional doses and pH 7-8).
Prevalence
Prevalence can either refer to the abundance of a certain pathogen in source
waters or to the prevalence of infection within a certain population.
The waterborne pathogens discussed are ubiquitous in source waters across
the globe and concentrations may vary considerably over time. Short-term
events can cause large spikes in concentration. Determination of the specific
pathogen load in any source water involves sampling and monitoring using a
method of direct detection.
Prevalence in a population provides an indication of the level of disease,
and it can be utilized in epidemiological studies over time to determine whether
public health interventions are reducing disease incidence. Prevalence of infec-
tion can be measured by testing either fecal samples for excreted pathogens
or serum samples for the presence of antibodies. Analysis of fecal samples is
useful in an outbreak. Alternatively, serological studies provide an overview of
the proportion of a population that has been exposed to a particular pathogen,
though this approach assumes that the pathogen confers long-lived immunity,
which is not the case for all waterborne pathogens.