- the sterile field
- the non-sterile surroundings
Any non-sterile item entering the sterile field renders it non-sterile; and stringent efforts and protocols [1,2] are made to ensure that this does not happen.
The protocols above extend via simply analogy [3,4] to information handling and information privacy.
- Any body of data which is containing certain amounts and kinds of sensitive data we can consider to be non-sterile - assume for a moment that certain bits and bytes are infectious (great analogy!).
- Everyone working with information is required to remain sterile and uncontaminated.
- Information which is truly anonymous is sterile
- Mixing two sets of information produces a single set of new information which is as at least as unclean as the dirtiest set of data mixed, and usually more so!
- The higher the security classification the dirtier the information
Extending our analogy further we can protect the sterile field in two ways:
- ensuring that everyone in contact with the sterile field is sterile
- ensuring that the equipment entering the sterile field is sterile
- If two sets of data are to be mixed then ensure that the mixing occurs not in-situ but by generating a third data set kept separate from the two input sets
- Data can be made more sterile by removing information content. But, be warned that certain kinds of obfuscation are not effective, eg: hashing or encryption of fields might just hide the information content of that field but not the information content of the whole data set 
- Keep sterile and non-sterile data-sets apart, physically if possible
- Ensure that sterile and non-sterile data-sets have differing access permissions. Ideally different sets of people with access
- Clean up after yourself: secure data deletion, overwriting of memory, cache purges etc.
From a personnel point, in surgery precautions are made through restricting the persons inside the sterile field and even outside of this, basic precautions are taken in terms of protective clothing etc. While surgical attire might be overkill for office environments, the analogy here is that personnel with access to data have received the correct training and are aware of what data they can and can not use for various purposes.
In a surgical environment, everything entering and leaving the sterile field is checked and recorded. In an information systems environment this means logging of access so that when a breach of the sterile field occurs the route of the pathogen and its nature can be effectively tracked and cleaned.
 Infection Control Today - August 1, 2003 : Guidelines for Maintaining the Sterile Field
 Infection Control Today - November 7, 2006 - Best Practices in Maintaining the Sterile Field