Information contained in a single word or phrase is not always sufficient for understanding the value of a clinical variable; the context around the phrase is often essential in understanding the patient's clinical state. Among other things, contextual information is important for determining when the finding occurred and what anatomic location was involved.
Any expert system attempting to increase timeliness in outbreak detection must distinguish between findings that occurred in past history and current problems. For example, one of the variables in our SARS detector is whether the patient has an acute respiratory finding. The definition of acute is not straightforward. However, at the least, an NLP application attempting to determine the value of this variable should be able to accurately assign the value yes to pleuritic chest pain in sentence 13 and no to pneumonia in sentence 14.
(13) The patient presents today with pleuritic chest pain.
(14) She has a past history significant for pneumonia.
A physician reading a report uses contextual clues like the structure of a report to discriminate between acute or current findings and those in the past history. For example, a finding described in an ED report within a section that is titled "Past Medical History'' is probably a historical finding. A human may also use linguistic cues within sentences to determine whether a finding is current. For instance, in sentence 15, a physician would know that myocardial infarction occurred in the past history but that chest pain is a current finding.
(15) He has a past history significant for myocardial infarction, and presents to the ED today with chest pain.
Determining what findings are described in a patient report also entails discriminating current findings from future or hypothetical findings. In sentence 16, the instance of fever is described as a hypothetical finding, but shortness of breath is described as a finding that probably occurred at the current hospital visit.
(16) She should return for fever or exacerbation of her shortness of breath.
Some findings can occur with multiple anatomic locations. For detection of SARS, our expert system needs to know whether the edema described in sentence 17 was found in the lung or in the skin.
(17) Chest is edematous.
Sometimes the anatomic location is explicitly stated, as in sentence 18. Other times, the anatomic location is not explicitly stated (e.g., sentence 19). The context around the finding is important for disambiguating the anatomic location—even when a location is not explicitly stated.
(18) The lump on her back has not changed.
(19) Chest x-ray showed no mass.
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