Water and infection : Epidemiological studies of epidemic and endemic waterborne disease

Abstract

Infections transmitted by water continue to be a public health problem both in developing and in developed countries. In the developed countries, the classical waterborne diseases such as typhoid and cholera are almost eliminated, whereas other pathogens and challenges have emerged. <br><br>

The overall aim of the thesis was to investigate and describe aspects of water-associated infections in a Nordic setting. Contaminated water may act as a transmitter of infectious disease by various routes. Examples of both traditional routes and more recently recognised routes are illustrated. In addition, the thesis describes and evaluates the use of different epidemiological tools and study designs in investigating waterborne illness, and demonstrates how the approach is guided by the outbreak setting and the purpose of the investigation. <br><br>

This research focus on four areas; endemic waterborne disease, outbreaks caused by contaminated drinking water, outbreaks caused by produce irrigated with contaminated water and a description of an outbreak caused by inhalation of contaminated aerosolised water.<br><br>

The disease burden caused by non-outbreak related waterborne illness is difficult to estimate. We describe two studies linking endemic illness to drinking water. The first was an ecological study on environmental risk factors for campylobacteriosis in Sweden. Areas with longer water-distribution network and higher proportion with private water supply was associated with a higher rate of infection than areas with shorter distribution networks and public water supply. The second study found an increased risk of gastrointestinal illness following an episode of maintenance work or mains repair on the water distribution network.<br><br>

In the second part, we describe outbreaks caused by contaminated drinking water. Most waterborne outbreaks in Norway are linked to smaller waterworks with no or failing disinfection. We do, however, also experience larger outbreaks where the hygienic barriers are in place, exemplified by a Giardia outbreak linked to a waterworks supplying several thousand persons. Late detection lead to prolonged suffering and delay in treatment, and emphasizes the need for improved outbreak detection systems. <br><br>

In the third part, we describe two outbreaks caused by produce irrigated with contaminated water. Both outbreaks were caused by imported lettuce, and the pathogens involved were not endemic in the importing countries. The outbreaks illustrates that water safety is not only a national concern, and that waterborne pathogens that are not endemic may be introduced in new areas through imported produce. Due to increased trade and travel, international collaboration in infectious disease surveillance and control is important for effective prevention.<br><br>

The fourth part describes a different aspect of waterborne transmission, illustrated in an outbreak of legionellosis caused by inhalation of contaminated aerosolised water. The investigation identified a new source of Legionella transmission; an industrial air scrubber. Technological developments used to improve living conditions, such as air conditioning systems, and protect the environment through “washing” polluted air in scrubbers, creates new ecological niches where aquatic microorganisms can multiply and be disseminated and cause disease. A thorough risk assessment needs to be carried out during the development and implementation of such systems, so that effective preventive measures can be put in place.<br><br>

In the final chapter we give some general recommendations and suggest some further studies to better understand the burden of waterborne disease, and some approaches to improve outbreak detection and investigation.