Waterborne Pathogens

Question 1

Emerging waterborne pathogens and related diseases

Answer 1

Infections can be caused by ingestion, contact with contaminated water or airborne (bacteria, viruses, protozoa, helminths)

• E.coli -> acute (bloody) diarrhea, gastroenteritis
• legionella -> acute respiratory illness, pneumonia
• salmonella -> typhoid fever
• hepatitis -> hepatitis

Question 2

Detection methods of waterborne pathogens

Answer 2

Based on detection of general indicators of faecal pollution as drinking water quality measure. Faecal indicator bacteria (FIB)
- Faecal coliforms (eg E coli as general faecal indicator)
Why E coli?
- Prevalence in human and animal faeces
- Does not survive well outside intestinal tract so presence indicates recent pollution
- Detection methods are fast, affordable, …

Most probable Number (MPN):
method used to estimate the concentration of viable microorganisms in a sample by means of replicate liquid in ten-fold dilutions (log). It is commonly used in estimating microbial populations in soils, waters, and is particularly useful with samples that contain particulate material that interferes with plate count enumeration methods.
Water to be tested is diluted serially and inoculated in lactose broth, E coli if present in water utilize the lactose present in the medium to produce acid and gas. The presence of acid is indicated by color change of the medium and the presence of gas is detected as gas bubbles collected in the inverted durham tube present in the medium. The number of faecal coliforms is determined by counting the number of tubes giving positive reaction (i.e both color change and gas production) and comparing the pattern of positive results (the number of tubes showing growth at each dilution) with standard statistical tables

FISH (fluorescence in situ hybridisation)
- Hybridisation with fluorescent probes -> allows quantificiation
- Unable to distinguish viable/non viable cells

Biosensor based methods
- Combine biochemical recognition element with physical transducer -> converts chemical response to electrical response
- fast, real time, specific, sensitive

Question 3

What is quantitative microbial risk assessment

Answer 3

= quantitative assessment process to estimate the health risks or illness rates of human exposure to particular pathogens

Combines dose response information and information on distribution -> demonstrates if health targets are met (target is less than 1 infection per 10.000 persons per year)

Question 4

Steps for quantitative microbial risk assessment

Answer 4

• Hazard identification: pathogen detection/identification, quantification, etiologies
• Exposure assessment: probability of pathogen concentration, exposure pathways, (aerosol, drinking water, …), duration of exposure
• Dose-response assessment: probability of pathogen ingested (= dose), relationship between dose and disease in the exposed population
• Risk characterisation: estimate individual/population level risks -> possible impacts on health
• Risk management and communication: implement solutions and communication to population and stakeholders, legislation

Question 5

Challenges of detection methods for waterborne pathogens

Answer 5

There is no unified method for all pathogenic microorganisms of interest.

• Non-enteric pathogens not covered
• End-product testing for FIB is too late, water is already consumed
• Viruses can cause outbreaks without FIB
• It is a reactive check, not a proactive control of the water quality
• Many coliforms have been shown to not be specific for faeces, even E coli can grow in natural env.
• In developed countries, viruses and parasitic protozoa have been found to be more common as etiological agents than bacteria