Evaluation of the New York State Department of Health Legionellosis Surveillance System

BACKGROUND: Legionellosis has been reportable to the New York State Department of Health (NYSDOH) since 1986. The Communicable Disease Electronic Surveillance System (CDESS) contains data on cases back to 1997. Since 2006, all positive laboratory test results have been reported via the Electronic Clinical Laboratory Reporting System, and electronically transferred to CDESS. Investigations of all cases of legionellosis are conducted by local health departments (LHDs). This evaluation assesses current capabilities and limitations of the system and provides recommendations to improve future use. 

METHODS: Evaluation was conducted using the CDC Guidelines for Evaluating Public Health Surveillance Systems. Data from 1997-2012 were extracted and analyzed using SAS 9.3. To evaluate timeliness, median times between symptom onset date, diagnosis date, date report received by LHD, and investigation initiation date were calculated. Data quality was assessed by completeness of key questions on the supplemental interview form. Sensitivity was assessed by comparing 2012 CDESS cases to 2012 statewide hospital discharge data (HDD) with the ICD-9 code for Legionnaires’ Disease (LD) (482.84). Positive predictive values (PPVs) were calculated as the percentage of cases reported as confirmed that had laboratory confirmation and percentage of cases that met CSTE clinical classification. Simplicity was evaluated by assessing information flow and level of integration with other information systems. Flexibility was assessed by ability to add or modify variables.

RESULTS:  From 1997-2012, 3440 confirmed cases of legionellosis were reported to the NYSDOH. The median number of days in all time intervals decreased from 1997-2012, indicating improvements in processing and investigation. Data quality improved for 60% of variables assessed, stayed constant for 17%, and decreased for 23%. The sensitivity analysis found that 222 of 249 patients with an ICD-9 code for LD from the HDD were confirmed cases in CDESS (89.2%). PPV was high (98.9%) for LD CSTE clinical classification and confirmatory laboratory testing (>90% for 10 of the last 12 years with data available). The system is well integrated with other electronic health systems and is flexible because it was developed and managed within the DOH.

CONCLUSIONS:  From 1997–2012, the legionellosis surveillance system demonstrated a marked improvement in timeliness and data quality, paralleling a period of electronic data integration and improvement. Sensitivity and PPV were high, and simplicity and flexibility were good. Recording time stamps of when interviews were conducted or reasons why interviews could not be completed could improve evaluation of data processing and interviewing efficiency.