Firearm-Related Deaths and Hospitalizations -- Wisconsin, 1994

Firearm-related injuries are a major cause of premature deaths in the United States (1). Although state-based vital records systems monitor fatal injuries, few surveillance systems exist to monitor nonfatal firearm-related injuries (2). Wisconsin is one of seven states funded by CDC cooperative agreements to establish firearm-related injury surveillance systems. Wisconsin's system, which links hospital discharge records and vital records, uses external cause of injury codes (E-codes) for case identification. This report describes the surveillance system and findings for 1994.

All Wisconsin hospitals are required to report E-codes for hospitalized patients to the state's hospital discharge database. E-codes, which are part of the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) injury classification scheme, were used to classify the intent of the perpetrator and the type of firearm discharged. E-codes used to classify intent include E922.0-9 (unintentional), E955.0-4 (suicide), E965.0-4 (assault), E985.0-4 (unknown intent), and E970 (legal intervention). Completeness of E-code reporting for all injury-related hospitalizations was greater than 90% for 1994 (Wisconsin Office of Health Care Information, unpublished data, 1995).

To assess only incident events, all five elective admissions were omitted. Duplicate entries in the database from interhospital inpatient transfers and readmissions were identified using an encrypted patient identifier, date of birth, sex, race, zip code, and admission/discharge dates. Eighty-eight patient records matched on at least five of these six variables; the second admission for each of these records was excluded because it did not represent an incident event.

In this surveillance system, a case is defined as an injury to a Wisconsin resident resulting from discharge of a firearm that led to hospitalization and/or death in Wisconsin. Case-patients in the vital statistics database were identified through the underlying cause-of-death code on death certificates. To eliminate duplicate entries in the combined hospital discharge-vital records database, in-hospital death records were linked to death certificates using encrypted patient identifier, birth date, death date, sex, race, hospital identifier, and zip code. Of the 54 hospital discharge records that indicated the patient had died, 51 matched in the vital records database on at least five of the seven variables, including birth and death dates. The remaining three were retained in the analysis as nonfatal hospitalizations.

After elimination of elective, transfer, and readmissions, 567 persons were admitted to Wisconsin hospitals in 1994 for firearm-related injuries. Of these, 51 (9%) cases were fatal and 516 (91%) nonfatal. Of the 511 firearm-related deaths reported in 1994, 51 (10%) occurred in a hospital.

The overall rates of nonfatal hospitalizations and fatalities from firearm injuries were 10.2 and 10.1 per 100,000 population, respectively (Table_1). The overall assault rate with firearms was 8.8, representing 44% of all firearm-related injuries. The rate of firearm injuries with suicidal intent was 7.4, representing 36% of all firearm-related injuries. Suicides accounted for 64% of all firearm-related deaths, and nonfatal attempts accounted for 8% of hospitalizations. In comparison, assaults accounted for 28% of firearm-related deaths and 59% of nonfatal hospitalizations.

The type of firearm used was specified for a high proportion of suicide-related firearm injuries but a low proportion of assaults. For suicide-related firearm injuries, long guns (rifle or shotgun) were used in 52% and handguns in 36%; 12% were unspecified (Table_2). The type of firearm was reported in 39% of all assault injuries. An autopsy was performed on all 142 persons who died from assault; the type of firearm was reported for 23%.

Reported by: S Hargarten, MD, Medical College of Wisconsin, Milwaukee; L Haskins, L Stahlsmith, MS, B Chatterjee, MS, J Morgan, P Remington, MD, Section of Emergency Medical Svcs, Bur of Public Health, Wisconsin Dept of Health and Family Svcs; R Nashold, P Peterson, Wisconsin Center for Health Statistics; T Karlson, PhD, Wisconsin Office of Health Care Information. Div of Violence Prevention, National Center for Injury Prevention and Control; Div of Applied Public Health Training (proposed), Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: Firearm-related injury data are important in identifying risk factors and in developing firearm- and violence-related injury-prevention programs. Linkage of hospital discharge and vital records databases in the Wisconsin Firearms Injury Surveillance System provides more complete data about firearm-related injuries in Wisconsin than does vital records data alone. The inclusion of nonfatal firearm-related injuries requiring hospitalization doubled the number of firearm-related injuries in the surveillance system (from 511 to 1027). In addition, approximately 9% of persons hospitalized for firearm-related injuries died during the hospitalization, a finding consistent with previous reports (3).

The surveillance system does not capture medical encounters that do not result in hospitalizations or death. However, an estimated 57% of all patients treated for a firearm-related injury are hospitalized. During 1994 in Wisconsin, based on 567 hospitalizations, an estimated 430 additional persons had firearm-related injuries that were treated without hospitalization (3).

Two factors have enabled Wisconsin to incorporate nonfatal firearm-related hospitalizations into the firearm-related injury surveillance system. First, mandatory E-code reporting in hospital discharge records with a high completeness of reporting provides previously unavailable data about injuries requiring hospitalization. Second, patient identifiers common to both hospital discharge and vital records databases allow linkage within and between the two databases. Elimination of duplicates enables more accurate estimates of firearm-related injury incidence.

The findings in this report are subject to at least three limitations. First, social, legal, and insurance concerns may prevent accurate reporting to medical providers and examiners. Second, missing or inadequate documentation by medical providers may preclude a specific E-code assignment (4). Complete E-code assignment may be impossible if the bullet caliber is known but not the type of firearm (e.g., 22 caliber). Third, coding instructions limit E-code utility. For example, when the intent of the injury is unknown, ICD-9 instructions are for deaths to be coded as unknown intention, whereas nonfatal injuries are to be coded as unintentional. This directive from the ICD-9-CM manual for coding nonfatal injuries is not uniformly followed; however, it probably overestimates the number of unintentional, nonfatal firearm-related injuries.

The use of E-codes and linkage of hospital discharge and vital records databases has enabled identification at the state level of firearm-related injuries resulting in hospitalization or death. This surveillance system is passive, flexible, inexpensive, and timely (5). Information from the system can aid in the accurate description of the at-risk population, improve cost estimates, and assist community leaders in evaluating firearm-injury trends and the impact of prevention programs.

References

1. CDC. Firearm-related years of potential life lost before age 65 years -- United States, 1980-1991. MMWR 1994;43:609-11.

2. Kellermann AL, Lee RK, Mercy JA, Banton J. The epidemiologic basis for the prevention of firearm injuries. Annu Rev Public Health 1991;12:17-40.

3. Annest JL, Mercy JA, Gibson DR, Ryan GW. National estimates of nonfatal firearm-related injuries. JAMA 1995;273:1749-54.

4. Sniezek JE, Finklea JF, Graitcer PL. Injury coding and hospital discharge data: beyond the tip of the iceberg. JAMA 1989;262: 2270-2.

5. CDC. Guidelines for evaluating surveillance systems. MMWR 1988;37(no. S-5).

TABLE 1. Number, percentage, and rate * of firearm-related injury hospitalizations and
deaths, by intent of injury -- Wisconsin, 1994
====================================================================================================
                                   Nonfatal
                               hospitalizations              Deaths                  Total
                              -------------------      -------------------    --------------------
Intent of injury              No.    (%)     Rate      No.    (%)     Rate     No.     (%)    Rate
--------------------------------------------------------------------------------------------------
Unintentional                 124   ( 24)     2.4       31   (  6)     0.6     155   ( 15)     3.0
Assault                       303   ( 59)     6.0      142   ( 28)     2.8     445   ( 44)     8.8
Suicide/attempted suicide      44   (  8)     0.9      329   ( 64)     6.5     373   ( 36)     7.4
Unknown intention              41   (  8)     0.9        3   ( <1)    <0.1      44   (  4)     0.9
Legal intervention              4   ( <1)    <0.1        6   (  1)     0.1      10   (  1)     0.2

Total                         516   (100)    10.2      511   (100)    10.1    1027   (100)    20.3
--------------------------------------------------------------------------------------------------
* Per 100,000 population.
====================================================================================================

TABLE 2. Number and percentage of firearm-related injury hospitalizations and deaths,
by weapon type and intent of injury -- Wisconsin, 1994
========================================================================================
                                           Nonfatal
                                   hospitalizations        Deaths            Total
                                   ----------------     ------------      ------------
Intent of injury/Type of weapon       No.     (%)       No.     (%)       No.     (%)
--------------------------------------------------------------------------------------
Attempted suicide/suicide

  Handgun                              12    ( 27)      123    ( 37)      135    ( 36)
  Rifle or shotgun                     20    ( 46)      174    ( 53)      194    ( 52)
  Unspecified                          12    ( 27)       32    ( 10)       44    ( 12)

Total                                  44    (100)      329    (100)      373    (100)

Assault

  Handgun                             126    ( 42)       18    ( 13)      144    ( 32)
  Rifle or shotgun                     16    (  5)       14    ( 10)       30    (  7)
  Unspecified                         161    ( 53)      110    ( 77)      271    ( 61)

Total                                 303    (100)      142    (100)      445    (100)
--------------------------------------------------------------------------------------
========================================================================================

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