Data for injuries occurring from 1998 through 2008 were obtained from: (1) the Washington State Trauma Registry (WTR), maintained by the Washington State Department of Health, and (2) WC claims, maintained by the Washington State Department of Labor and Industries (L&I). This study was approved by the Washington State IRB.

The WTR contains reporting data for traumatic injuries meeting specific inclusion criteria from all state-designated acute trauma facilities. For most of the years of this study, reports were mandatory for adult patients who (1) were discharged with ICD-9-CM diagnosis codes of 800–904 or 910–959 (injuries), 994.1 (drowning), 994.7 (asphyxiation), or 994.8 (electrocution), and (2) met at least one of the following criteria: trauma resuscitation team activation, dead on arrival, death during the emergency department (ED) visit or associated hospital stay, interfacility transfer by Emergency Medical Services (EMS) or ambulance, or inpatient admission of at least 48 hours. The WTR contains no information about occupation or industry, but does contain a work-relatedness field that has been shown to be highly sensitive and specific in identifying work-related injuries.¹³ In a nationwide survey conducted in 2004 by Mann, et al., the WTR trauma manager estimated that the WTR captured about 85% of trauma victims with injuries satisfying registry inclusion criteria.¹⁴ However, the WTR does not capture data for the many occupational injuries that do not meet inclusion criteria.¹⁵ In addition, occupational fatalities can occur in any setting and only those occurring after contact with the EMS and trauma system are reported to the WTR.⁵

Washington State has a single payer WC system (the State Fund) that covers approximately 70% of workers specified by the Industrial Insurance Act.¹⁶ Self-insured employers account for the remaining 30%. Compensable State Fund and self-insured WC claims were obtained from L&I, excluding injuries among workers younger than 16 and injuries occurring outside Washington State. (Compensable WC claims include claims for fatalities, total permanent disability, and those involving compensation for work missed due to the injury.) The study excluded WC claims with special confidentiality-related restrictions and medical aid-only claims. Medical aid-only claims cover medical treatment but do not involve time-loss payments because the injury did not cause any missed work days after the initial three-day post-injury waiting period. A preliminary assessment found that very few medical aid-only claims linked to the relatively severe traumatic injuries reported to the WTR.

Records were linked and deduplicated using The Link King, a public domain software program developed in Washington State for deterministic and probabilistic linkage of administrative records.¹⁷ Direct personal identifiers were available for the linking procedures. All non-exact matches were reviewed by the first author for plausibility. This resulted in 6,673 work-related injury events (for 6,645 workers) having both WTR and WC data available. Further detail about the data sources and linkage procedures can be found in previous publications.^13,18

TBI was identified following the CDC case definition: the presence of any ICD-9-CM code of 800.0–801.9, 803.0–804.9, 850.0–854.1, 950.1–950.3, or 959.01 in any of the 27 WTR ICD-9-CM diagnosis fields.^1,10 These codes were generated for clinical descriptive purposes, generally by the trauma surgeons and/or trauma registrars (in contrast to the ICD-9-CM codes in hospital discharge or workers’ compensation data that are generated primarily for billing purposes). The WTR has conducted periodic validity studies assessing factors such as coding accuracy. The software used by the hospitals to collect and submit data to the registry contains logic checks and error checks that facilitate data quality and completeness.

Isolated TBI was defined as TBI that did not have any maximum Abbreviated Injury Scale (AIS) score greater than 1 (no more than minor injury) in body regions other than the head/neck, as well as no indication of additional moderate extracranial injury in the head/neck region (e.g., facial fractures, cervical spine injuries). TBI with other trauma was defined as TBI that had at least one maximum AIS score greater than 1 in a body region other than the head/neck or an ICD-9-CM code in the head/neck region indicating at least moderate extracranial injury.

Fatalities were defined as workers who died prior to or during the initial hospitalization according to WTR data, or whose WC claim was classified as a fatality. Fatalities would not be captured by the WTR if there was no trauma hospital involvement (e.g., direct transport to a morgue or coroner). Cause of injury was based on the ICD-9-CM external cause of injury codes (E codes) from WTR records and categorized according to CDC recommendations.¹⁹

L&I uses the 2007 version of the OIICS to identify and record injury/illness characteristics.²⁰ OIICS codes were available for essentially all State Fund and self-insured claims. Due to missing OIICS nature of injury or part of body codes, 34 injury events (0.5%) were excluded from these analyses (9 were nonfatal TBI cases and 3 were fatal TBI cases).

Solely for purposes of this study, six OIICS-based TBI case definitions were defined as shown in Figure 1. Case definition 1 (CD1) was the narrowest, and CD2 through CD6 were progressively less restrictive (CD6 was so loose as to arguably be meaningless with respect to TBI, and is presented only for purposes of illustration).

WTR-based ICD-9-CM codes were used as the gold standard for identification of TBI cases. Counts of TBI captured by various combinations of OIICS nature and part of body categories were calculated separately for: (1) all TBI, (2) fatal TBI, and (3) isolated TBI. Sensitivity, specificity, area under the curve (AUC) using receiver operating characteristic (ROC) curves, positive predictive value (PV+), and negative predictive value (PV−) were estimated for each of the six case definitions. The number and percent of cases captured by each of the six case definitions were calculated for several subsets of TBI (fatal, nonfatal, isolated TBI, TBI with other trauma).

Analyses were performed using Stata/SE 11.2 for Windows (StataCorp LP, College Station, TX). The Stata user-written program -diagt- was used to calculate case classification statistics.²¹

This study constitutes a preliminary and novel effort to explore and describe challenges with respect to developing an OIICS-based case definition for fatal/nonfatal TBI and the potential implications for prevention efforts. This study relied on clinical diagnosis codes from a trauma registry combined with WC claims data. Most states maintain a trauma registry, and researchers in several states (e.g., Alaska, Illinois, and Washington) have begun to explore these registries as a resource for occupational injury surveillance and research.^{13,18,28–30} However, few states have population-based WC data in addition to a well-developed trauma registry. Leveraging this unusual combination of circumstances is a major strength of this study.

This study relied on a relatively severe group of injuries reported to a trauma registry, and those injured may have been more likely to have sustained TBI and/or multiple injuries compared with a more general occupational injury sample. In this study, about 20% of all injuries and 60% of fatal injuries involved TBI, compared with a CDC estimate that TBI contributes to 31% of all injury-related deaths.¹ An Ontario-based study used coroner’s records to determine that TBI contributed to 45% of work-related fatalities.³¹ NIOSH researchers found that TBI accounted for 22% of all occupational injury deaths and 46% of fatal falls (note the important distinction between “contributed to” and “accounted for”).⁶

We do not presume to recommend any specific OIICS-based case definition for use in TBI surveillance. Doing so would require further expert review for face validity, as well as validation in data sets more representative of the spectrum of occupational injuries. Some of the case definitions used in this study might be less specific for TBI in a broader occupational injury sample. There are many possible combinations of OIICS codes that could be contemplated for inclusion. For example, the case definitions used in this study did not include gunshots to the head for simplicity’s sake, although this was done in a NIOSH study of fatal occupational TBI (using nature=036 and part of body=00 or 01 or 08).⁶ Doing so would have made little difference for this study; there were only four such cases over all 11 years (all were classified as TBI per WTR data, and two were fatal). It is likely that many such cases were pronounced dead at the scene, never transported to a trauma hospital, and thus never reported to the trauma registry. There are likely other examples of categories that could and should be considered for inclusion in a final TBI case definition.

This study captured only a portion of the work-related TBI in Washington State, and the numbers presented were not intended to describe incidence. This study was limited to traumatic injuries eligible for and included in the WTR and required linkage to a compensable WC claim. Thus, minor injuries, injuries not treated at a designated trauma hospital or not reported to the trauma registry, as well as injuries not reported to WC or not covered by WC (e.g., federal workers, domestic workers, the self-employed, etc.) would not have been included.