Consistency can be more useful than sheer size
A stable group of sites with clear procedures can help track changes over time. Adding more sites may improve coverage, but it can also change the observed mix of patients and create an apparent trend.
Site participation belongs in the interpretation.
Ask what the network captures
- Which regions and facility types participate?
- Who seeks care at those sites?
- Are samples selected consistently?
- Are reporting completeness and methods stable?
- How are national or regional summaries weighted, if at all?
These questions define the scope of the evidence.
A local surge may be missed
If an event occurs mainly outside participating sites, the network may detect it late or not at all. A flat sentinel trend does not prove that every community is unchanged.
Conversely, an increase at selected sites may require investigation before being generalized more broadly.
Keep estimates and signals separate
A surveillance system may be designed primarily to detect changes, characterize circulating pathogens, or estimate burden. Those are different objectives. A network useful for one may need additional methods for another.
Describe the participating system and its purpose when presenting the result. The value of selected-site surveillance comes from a well-understood observation process, not from pretending the selection does not matter.
