Issue 4: Microbiological

Worldwide, the WHO estimates that food- and water-borne infectious diseases caused 3 million deaths in 1995, and 80% of these were to children less than 5 years of age. It has been estimated that of 99 million reported gastrointestinal infections in the USA each year, as many as one-third may involve exposure to waterborne pathogens. In the USA, the annual costs (medical costs and lost productivity) of common intestinal infections were estimated to be $23 billion (food- and waterborne).

Waterborne diseases may involve bacteria (such as Shigella, Campylobacter or Salmonella) or viruses (such as Norwalk or hepatitis A) but the public health spotlight is currently on protozoans. One protozoan, Cryptosporidium, has a life cycle that involves asexual reproduction within cells lining the intestinal tract, and a sexual reproduction phase that results in the production of oocysts that are released in the faeces. Other protozoans that can also cause diarrhoeal diseases but are less common are Cyclospora, Isospora and microsporidia; their life cycles are similar, though the oocysts may not be infectious when passed in the faeces. Persons with compromised immune systems are especially susceptible to microbial infections; it is now estimated that the annual rate of cryptosporidial infection among AIDS patients may approach 5 to 10%.

The source of microbiological pollution is often inadequately treated human sewage or runoff from animal husbandry facilities into streams or lakes; in addition, some microbial populations can increase in drinking water distribution systems. Other factors may also influence microbial levels:

(1) Wild animals are a reservoir for bacteria or protozoa that can infect humans

(2) Variations in turbidity or water chemistry can affect bacterial densities

(3) Algal blooms may increase bacterial abundance.

GIWA definition

Microbial pollution refers to the adverse effects of microbial constituents of human sewage released to water bodies.

There are few commonly available direct indicators of microbial damage to marine organisms. The microbiological indicators employed here are those commonly available to protect human health and have been supplied as a surrogate assuming various severities of environmental impact.

Environmental impacts

1. Aquatic organism infections and diseases

Indicators

The following are environmental impact indicators for the microbiological issue.

Select the environmental impact indicators that are relevant from the list below and input data into the appropriate indicator sheets.

Pollution

Fisheries

Biological

Proxy indicator of microbiological pollution