The place and time of sampling for environmental surveillance
The options for sampling sites, frequency and timing depend on the environmental compartment of interest. For all environmental compartments it is important to consider the parameters explored below.
Position with respect to the point of emission
Because many of the study objectives are related to measuring AMR from human activities or exposure to AMR in the environment, mapping the study area and identifying potential sources of contamination is vital for environmental studies. These emissions are a result of human activities such as:
- farming where antimicrobials are used
- factories that produce antimicrobials
- hospitals that take care of patients carrying AMR and residues
- surface water receiving treated or untreated sewage from abattoirs or wet markets.
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What control could you consider including in your sampling of a potential contamination source?
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A sample upstream of the prospective source of contamination (if a river is studied), or from a site not under the influence of the studied point source. This gives you a baseline to assess the level of hazardous emission.
Time of the day or year
Daily and yearly (seasonal) patterns can significantly influence the presence, spread and behaviour of AMR microbes in the environment. The main factors related to time of the day or year affecting these patterns are:
- temperature
- precipitation
- human and animal activity.
The following table summarises how each of these factors affects AMR dynamics.
| Factor | How it affects AMR dynamics |
|---|---|
| Temperature | Bacterial growth is affected by temperature: bacteria multiply faster in warmer temperatures. On the other hand, bacteria are also inactivated more quickly at higher temperatures. Time of the day and season exhibit different temperatures. |
| Precipitation | Rainfall, flooding or droughts. Excess water can overwhelm sewerage systems, causing release of polluted water. Droughts lessen water flows so limit the spread of water-borne resistance, but can also lead to higher concentrations of AMR bacteria due to a reduction of dilution by rainwater. Precipitation varies across seasons and regions. |
| Human and animal activity | Human and animal activity is not stable over time of the day or year but is clustered at times (e.g. mornings) or places (e.g. urban vs rural areas). Activity is a source of emission of AMR and/or residues. The more humans and animals are locally active the more faeces they produce. |
All these factors can either promote or limit the spread of AMR microbes. Understanding these variations in the area and time of study allows for more discriminating hypotheses to be formulated, and better planning of the surveillance. This knowledge also suggests which AMR indicators to assess and their potential prevalence. It also helps to identify high-risk periods/peaks.
Another important aspect to consider is that all these factors are being affected by climate change, both now and possibly more so in the future.
When you’ve read this section you should return to Section 9 of the course.
Further examples of water surveillance
