Health Risk Management

A barrier is a part of the treatment or handling chain of a sanitation system that substantially reduces the number of pathogens present in excreta. The barrier function is normally expressed in log-terms, where one log is similar to a 90% reduction, two logs similar to 99% reduction and so on. In the technical barriers, the reduction can be simplified to occur through different treatment processes. There is an additional risk of disease transmission related to the usage of sanitation system as well as the handling or use of the end products. These relate to environmental persistence and die-off, dilution factors, exposure and the dose that humans are exposed to (see also waterborne diseases pathogens and contaminants).

Barriers to protect oneself from infection are needed at all different points of exposure and for different exposure groups, i.e., those using the system, those handling the end products or those consuming crops fertilised with them.

A system for the safe disposal and reuse of human excreta and wastewater should not be based on a single barrier such as treatment, but that a multi-barrier approach is required to effectively eliminate and/or inactivate the different hazardous microorganisms spread through various routes as shown in the figure below (CARR 2001) and to obtain a high level of reliability. Achieving the objective of the multi-barrier approach requires a paradigm shift from the assessment of sanitation technologies as technological units, to one that encapsulates the system itself and human behaviour.

The transmission routes of excreta related disease, exposure points and the health risk factors involved are directly interlinked. The transmission of excreta related pathogens may be either primary (direct exposure) and/or secondary, (exposure through an external route). Primary transmission includes person to person contact, including short distance airborne transmission. Secondary transmission includes vehicle-borne (food, water etc.), vector borne and airborne long-distance transmission.

Closely related to the various transmission pathways are the following critical questions that need to be addressed in identifying the severity of the health risk associated with a particular pathway:

• WHO is exposed? This defines the groups that potentially are at risk.
• HOW MANY people (individuals) are likely to be exposed directly or indirectly? This may include the individual users, but as well maintenance workers or the number of people that are consuming crops fertilised with treated excreta, or the people indirectly exposed due to contamination soil, surface/groundwater or from contaminated drinking water sources.
• WHERE does the exposure occur within the sanitation system? With this question, one follows the system from the user to the potential step of reuse or disposal and also account for secondary exposure that occurs due to environmental pollution.
• WHICH routes should we consider? Is it mainly due to direct contact? Is it due to contamination of crops, soil or water sources? Is it due to mosquito breeding and so on?
• HOW frequently does exposure occur? Is this every time, daily, weekly or perhaps just once a year? Even if exact figures cannot be obtained, it may be of value to at least have a “guesstimate” about the frequency of exposure.
• WHAT dose of exposure occurs? This is also difficult to estimate, since it heavily depends on the local situation. It will also differ between groups of individuals but even an rough estimate is of value if one wants to do an overall calculation of the risk of infection. Naturally, this risk based on the exposure value will differ dependent on the prior treatment. This part is heavily linked with the occurring practices.

In addition, different user and non-user groups may be affected. In this context these groups can be defined as users, workers, farmers and  the community. Special consideration should be given to vulnerable groups like children, the elderly or people with other underlying disease.

• A USER is the person who uses the technology on a regular basis.
• A WORKER is a person who is responsible for maintaining, cleaning, operating or emptying the technology. However to avoid ambiguity, the emptying of a given technology is not addressed in the technology description, but is considered under the Function group ‘conveyance’.
• A FARMER is the person who is using the products generated (though that could be the same person as the user or the worker, for example, if the same person uses, cleans, empties and applies the products the different parts of the sanitation system. This group is only applicable to the category of use and/or disposal.
• A COMMUNITY includes anyone who is living near to, or downstream from the technology, and may be passively affected. ‘Community’ also includes anyone who consumes products (for example crops or fish) that are produced using sanitation products.

Sanitation is considered as a system comprising technical (functional groups) and non-technical components that work in synergy to safeguard human health. Each sanitation technology is related to this grouping or components.

Technologies are defined as the specific infrastructure, methods, or services that are designed to contain, transform, or transport products to another functional group or component. Five main functional groups make up a full sanitation systems:

1. User interface (or toilet system)
2. Storage and treatment
3. conveyance collection
4. secondary treatment 
5. disposal and/or reuse

Each of the functional groups may be represented by different technologies that are chosen depending on the local context. The selected technology within each of the functional groups will govern the overall reduction efficiency and the likelihood of disease transmission. Each is linked to critical points where pathogens may be transmitted or controlled (see also toilet systems).

Furthermore, the extent of human health protection by the sanitation system relates to non-technical socio-cultural aspects linked to specific features of the system, e.g. traditions, local believes, behaviours or taboos, or also predominant hygiene practices. These may further reduce (or sometimes elevate) exposure to pathogens at these critical points or as end-use related risks.

An example of such socio-cultural aspects are the Koranic edict where excreta are regarded as impure (najassa) and its use only permitted when the najassa is removed (FARUQUI 2001). Similarly, the Luo of western Kenya dispose of children’s faeces by digging and burying. This further relates to raining. Infants are trained to defecate in a special place and inform their care-takers so that the faeces are disposed of (ALMEDOM 1996) (see also sociocultural issues).

Cultures or traditions may also involve perception that exposes people to disease causing pathogens. This is the situation with child faeces which in other cultures are perceived as harmless, also when diarrhoeal diseases are prevalent. When mothers in areas with high prevalence of childhood diarrhoea are asked about the cause of the disease, they often blame it another factors than the poor handling of child faeces or poor hand washing practices (see also hygiene frameworks and approaches).