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ISDS 2016 Conference Abstracts

In Denial: Symptom Negation in New York City 
Emergency Department Chief Complaints
Jessica Sell*
Syndromic Surveillance, NYC DOHMH, Queens, NY, USA

Objective
To describe the effect of symptom negation in emergency 

department (ED) chief complaint data received by the New York City 
(NYC) Department of Health and Mental Hygiene (DOHMH), and to 
devise a solution to avoid syndrome and symptom misclassification 
for commonly used negations using SAS Perl Regular Expression 
(PRX) functions.

Introduction
In July 2016, 77% of ED data was transmitted daily via Health 

Level 7 (HL7) messages, compared to only 27% in July 2015 
(Figure). During this same period, chief complaint (CC) word count 
has increased from an average of 3.8 words to 6.0 words, with a 
twenty-fold increase in the appearance of the word “denies” in the 
chief complaint (Figure). While HL7 messages provide robust chief 
complaint data, this may also introduce errors that could lead to 
symptom and syndrome misclassification.

Methods
Using SAS 9.4 and Tableau 9.3, we examined data submissions 

from 14 EDs responsible for 97% of the occurrences of the word 
‘denies’ in chief complaints in July 2016.

To account for variation in chief complaint format among hospitals, 
we developed three PRX patterns to identify entire phrases in the 
chief complaint data field that began with conjugations of the word 
“deny” followed by various combinations of words, punctuation, 
spaces, and/or characters.

Pattern 1: '/DEN(Y|I(ES|ED|NG))(\s|\w|(\/)|(\+)|,|(\\)){1,}
((\.)|(\|)|($)|(;)|(\))|(-))/’

Pattern 2: '/DEN(Y|I(ES|ED|NG))(\s|\w|(\/)|(\+)|(\\)){1,}
((\.)|(\|)|($)|(;)|(\))|(-)|(,))/';

Pattern 3: '/DENIES:( |\w|\.|,){1,}/');
We separated the ‘denies’ statement from the chief complaint and 

identified commonly negated symptoms. We then defined symptoms 
using keyword searches of the chief complaint and the ‘denies’ 
statement. We compared symptom classification with and without 
the consideration of symptom negation.

Results
Of the 14 EDs analyzed, we applied pattern 1 to 8 of the ED’s, 

pattern 2 to 5 EDs, and patterns 2 and 3 to 1 ED. Approximately 
98% of denies statements were extracted from chief complaints. Only 
2% of symptom negation was not captured due to uncommon chief 
complaint format whose symptom negation didn’t meet one of the 
previously described PRX patterns.

The most common words associated with a “denies” statement 
were: pain, chest, fever, loc, shortness, breath, vomiting, nausea, 
travel, headache, recent, trauma, history, abdominal, injury, diarrhea, 
SOB (shortness of breath), V (vomit), Head, N (nausea), PMH (past 
medical history), suicidal, dizziness, homicidal and D (diarrhea) (see 
Table).

By not taking negation into consideration in symptom definitions, 
between 3.5% and 16.5% of symptom visits were misclassified. 
Symptom misclassification varied greatly by hospital, ranging from 
0% to 55%.

Conclusions
As hospitals in NYC implement HL7 messaging, symptom 

negation is becoming increasingly common in chief complaint data. 
Current symptom definitions are based on keyword searches that do 
not take into account symptom negations. This leads to symptom 
misclassification, and could potentially cause false signals or inflate 
syndrome baselines, causing true signals to go undetected. SAS PRX 
functions can be used to flexibly identify symptom negation patterns 
and exclude them from syndrome definitions. Future studies will 
quantify the effect symptom negation has had on signal frequency in 
NYC, and examine symptoms associated with other forms of negation 
such as “Personal Medical History”, “No” and “Negative.”

Most Common Symptoms Denied in Emergency Department Chief Complaints

Keywords
Symptom Negation; Perl Regular Expressions; HL7 Data

*Jessica Sell
E-mail: jsell@health.nyc.gov

Online Journal of Public Health Informatics * ISSN 1947-2579 * http://ojphi.org * 9(1):e70, 2017