Animal-Encounter Fatalities,United States,1999-2016: Cause of Death and Misreporting

Abstract

Objectives

Errors and misreporting on death certificates are common, along with potential inaccuracies in cause-of-death coding. We characterized and compared fatalities by animal-encounter mentions reported as underlying cause of death (UCD) with animal-encounter mentions reported as multiple cause of death (MCD) to determine factors associated with misreporting UCD.

Methods

We analyzed fatality data from 1999-2016 from the Centers for Disease Control and Prevention Wide-ranging ONline Data for Epidemiologic Research by UCD and MCD animal-encounter mentions (International Classification of Diseases, 10th Revision codes W53-59, X20-27 and X29, T63.0-63.6, T63.8-63.9, and T78.2-78.4). We examined differences in reporting by age, sex, race, autopsy (yes, no, unknown), allergic reactions, and toxicities.

Results

The number of animal-encounter mentions by UCD was 3638 (202 average per year) and by MCD was 4280 (238 average per year), a difference of 18% (n = 642; 36 average per year) by MCD analysis. The number of nonvenomous animal-encounter mentions increased 20% (from 2138 UCD to 2567 MCD), and the number of venomous animal-encounter mentions increased 14% (from 1500 UCD to 1713 MCD). Decedents aged ≥65 had the highest additional number of animal-encounter mentions among all age groups, primarily encounters with other reptiles (n = 113), other mammals (n = 71), and dogs (n = 42). Of 642 MCD additional animal-encounter mentions, heart disease (n = 211, 33%) and infections (n = 146, 23%) represented more than half of the UCD. Of 553 dog-encounter fatalities, 165 (30%) were among children aged ≤4.

Conclusions

Animal-encounter fatalities, analyzed by UCD alone, may be underreported. An initiating animal injury, complicated by comorbidities and fatality, may obscure the causal chain, resulting in misreporting UCD. Ongoing training for medical certifiers is recommended, highlighting accurate identification of UCD and contributing causes in the causal chain of death.

Keywords

animal-encounter fatalities animal-encounter deaths bites and stings underlying cause of death multiple cause of death death certification misreporting miscoding One Health

Encounters with animals (domestic or exotic pets or wild animals in the environment), whether intentional or unintentional, may result in injury or illness including pain, envenomation, allergic reactions, wounds, infection, disfigurement, and, rarely, death. Encounters with animals may result in psychological distress and economic hardship from loss of work and health care costs. Injuries or death from animal encounters may be initiated by a scratch, a sting, or a bite or by being stepped on, fallen on, thrown off, butted, rammed, gored, crushed, asphyxiated, or envenomed. Contaminated wounds may result in life-threatening infections and sepsis. In some instances, anaphylactic reactions may occur among people sensitized to an animal’s venom, saliva, dander, or urine.

Worldwide, millions of people are injured and more than 180 000 deaths occur annually from animal encounters.¹ Few deaths in the United States result from animal encounters. The human–animal bond is a well-recognized mutually beneficial relationship that exemplifies One Health^2

-5 and includes emotional, psychological, and physical interactions of people and animals that are essential to the health and well-being of both species.⁶ People of all ages are at risk of fatal animal encounters and injuries and would benefit from targeted education to prevent dog bites and domestic, exotic, and wildlife animal encounters in the environment.^7

-10

In the United States, nonfatal injuries from animal encounters outnumber fatalities from animal encounters. The Centers for Disease Control and Prevention (CDC) and the World Health Organization estimate that each year in the United States, dogs bite approximately 4.5-4.7 million people.^1,11 Of these, nearly 885 000 seek medical care, resulting in an average of 323 000 emergency department visits, 30 000 reconstructive procedures, and 10-20 fatalities; 3%-18% of people with dog bites develop infections.^1,12 An additional 76 000 people in the United States have a nonfatal fall injury because of a dog or cat.¹³ In addition, about 1 million people are seen in US emergency departments yearly from non–canine animal-related injuries.¹⁴ From 2006 to 2008, about 48 000 people were hospitalized annually in the United States because of an adverse animal encounter.¹⁵

A comparison of 2 studies of US animal-encounter deaths coded as underlying cause of death (UCD) showed that the average number of deaths per year increased from 177 during 1991-2001 to 201 during 2008-2015.^16,17 One weakness of previously published studies of animal-encounter deaths in the United States is that only the UCD was reported and analyzed.^16
-18

The accuracy of death certification is essential, because the death certificate is a medical–legal document and source for state and national mortality statistics used to determine state and national health status, set public health goals, develop policy, and determine which medical conditions receive funding for research and development.^19,20 The animal encounter may be listed correctly on the death certificate as the UCD, incorrectly as the immediate cause of death, or as a contributing condition in the causal chain contributing to the immediate cause (ie, a multiple cause of death [MCD]).^21,22 For example, if a death certificate reported sepsis as the UCD when the injury that initiated the events resulting in death (the underlying cause) was an animal bite, the animal bite would not have been reported accurately with UCD analysis alone. We examined animal-encounter fatalities with International Classification of Diseases, 10th Revision (ICD-10) coded as UCD and reviewed animal-encounter codes listed as an important condition contributing to death on the death certificate, mentioned as an MCD rather than a UCD.²³

Methods

The CDC Wide-ranging ONline Data for Epidemiologic Research (WONDER) is a web application consisting of 20 applications of health-related public-use data of births, deaths, and cancer diagnoses in the United States.²⁴ We analyzed CDC WONDER public-use mortality data, which does not require institutional review board approval. We extracted data from CDC WONDER UCD and MCD databases. CDC WONDER compiles the death codes as stated on the death certificate (entity axis).²⁴ Extracted data consisted of animal-encounter deaths (W and X codes) and toxicity injury deaths (T codes) classified by ICD-10²³ for US residents from 1999 through 2016. CDC WONDER UCD and MCD databases contain county-level national mortality and population data based on death certificates for US residents of 50 states and the District of Columbia. Each death certificate indicates a single UCD with up to 20 MCDs (contributing causes) and demographic data.²⁴ We used Microsoft Excel (Microsoft Corp) for statistical calculations.

The UCD is defined by the ICD-10 instruction manual as “the disease or injury which initiated the train of morbid events leading directly to death, or the circumstances of the accident or violence which produced the fatal injury.”²² We analyzed UCD data that resulted from venomous or nonvenomous animal encounters by using the following ICD-10 codes: nonvenomous: W53 (bitten by rat), W54 (bitten or struck by dog), W55 (bitten or struck by other mammals—includes cats, horses, cows, other hoof stock, pigs, raccoons, and other mammals, without species distinction), W56 (contact with marine animal—nonvenomous—includes dolphins, orcas, sea lions, sharks, other fish, and other nonvenomous marine mammals), W57 (bitten or stung by nonvenomous insect and other nonvenomous arthropods), W58 (bitten or struck by crocodile or alligator), and W59 (bitten or crushed by other reptiles); venomous: X20 (contact with venomous snakes and lizards), X21 (contact with venomous spiders), X22 (contact with scorpions), X23 (contact with hornets, wasps, and bees), X24 (contact with centipedes and venomous millipedes [tropical]), X25 (contact with other specified venomous arthropods), X26 (contact with venomous marine animals and plants), X27 (contact with other specified venomous animals), and X29 (contact with unspecified venomous animal or plant). Exclusions included fatalities from ingesting poisonous animals or plants and fatalities related to transportation accidents (V80.0 [animal-rider or occupant of animal-drawn vehicle injured in transport accident]).^23,24

Evaluation of MCD coding is important to understand the causal chain or logical sequence of contributing conditions and the immediate cause that developed subsequent to the UCD (initiating event) and to reveal potential errors in UCD coding. According to the ICD-10 instruction manual, “Multiple-cause coding permits in-depth analysis of causes of death, for example of serious but avoidable complications of certain underlying causes, and the impact of coexisting conditions on the outcome of a disease process. Therefore, in mortality coding, both underlying cause and multiple causes should be recorded.”^21,22 The MCD database combines mortality frequencies for underlying causes, immediate causes, and contributing causes of death.²⁴

We compared MCD mortality data with mention of an animal encounter (ie, W and X ICD-10 codes) with UCD mortality data for the same ICD-10 codes to determine if additional animal-encounter mentions contributed to other UCD ICD-10 codes. For those additional animal-encounter mentions identified in the MCD analysis, we identified the UCD.

In addition, we reviewed MCD mortality data for mention of toxic effects of contact with venomous animals to determine if mortality frequencies corresponded with the frequency of UCD X codes. ICD-10 T63 codes included T63.0 (toxic effect of snake venom), T63.1 (toxic effect of venom of other reptiles), T63.2 (toxic effect of venom of scorpion), T63.3 (toxic effect of venom of spider), T63.4 (toxic effect of venom of other arthropods), T63.5 (toxic effect of contact with venomous fish), T63.6 (toxic effect of contact with other venomous marine animals), T63.8 (toxic effect of contact with other venomous animals), and T63.9 (toxic effect of contact with unspecified venomous animal).^23,24

Animal-encounter mortality calculations used CDC WONDER annual population numbers (US Census Bureau estimates of national, state, and county resident populations²⁵) and included frequencies, rates per 10 million population ([deaths/annual population] × 10⁷), and percentages of total animal-encounter mentions by UCD and MCD analysis, age (<1, 1-4, 5-9, 10-19, 20-34, 35-64, ≥65), sex (male, female), race (White, Black/African American, Asian/Pacific Islander, American Indian/Alaska Native), injury intent (if injury was intentional), and autopsy (yes, no, unknown).²⁴ Rates based on <20 events were considered unstable and therefore were not presented. We calculated differences in number, percentage, and ratio comparisons for deaths with animal-encounter mentions reported as UCD and for deaths with animal-encounter mentions reported as MCD.

Results

During the 18-year study period (1999-2016), a total of 3638 deaths were reported in the United States with a UCD ICD-10–coded animal encounter (Table 1; Figure 1). Fatal animal encounters caused an average of 202 deaths per year with UCD analysis and 238 deaths with MCD analysis. Nonvenomous animal-encounter deaths predominated.

Figure 1

Animal-encounter mentions (International Classification of Diseases, 10th Revision code²³) by underlying cause of death (UCD) and multiple cause of death (MCD), United States, 1999-2016. Data source: Centers for Disease Control and Prevention.²⁴

Table 1

Comparison of animal-encounter mentions reported as underlying cause of death (UCD) and multiple cause of death (MCD), by number, percentage difference, and rate ratio, United States, 1999-2016^a

Animal encounter (ICD-10 code)^b	Animal-encounter mentions
Animal encounter (ICD-10 code)^b	UCD, no.	MCD, no.	Difference, no.	% Difference	MCD/UCD, rate ratio
Nonvenomous animals
Bitten or struck by other mammals (W55)^c	1314	1432	118	9	1.09
Bitten or struck by dog (W54)	553	630	77	14	1.14
Bitten or stung by nonvenomous insect and other nonvenomous arthropods (W57)	155	245	90	58	1.58
Bitten or crushed by other reptiles (W59)	78	206	128	164	2.64
Contact with marine animal (W56)^d	23	31	8	35	1.35
Bitten or struck by crocodile or alligator (W58)	12	13	1	8	1.08
Bitten by rat (W53)	3	10	7	233	3.33
Total nonvenomous	2138	2567	429	20	1.20
Venomous animals
Contact with hornets, wasps, and bees (X23)	1063	1150	87	8	1.08
Contact with other specified venomous arthropods (X25)	157	180	23	15	1.15
Contact with venomous spiders (X21)	124	197	73	59	1.59
Contact with venomous snakes and lizards (X20)	112	129	17	15	1.15
Contact with unspecified venomous animal or plant (X29)	31	40	9	29	1.29
Contact with scorpions (X22)	7	8	1	14	1.14
Contact with centipedes and venomous millipedes (tropical) (X24)	5	7	2	40	1.40
Contact with venomous marine animals and plants (X26)	1	2	1	100	2.00
Contact with other specified venomous animals (X27)	0	0	0	0	0
Total venomous	1500	1713	213	14	1.14
Total	3638	4280	642	18	1.18

Abbreviation: ICD-10, International Classification of Diseases, 10th Revision.

^aData source: Centers for Disease Control and Prevention.²⁴

^bData source: National Center for Health Statistics.²³

^cIncludes cats, horses, cows, other hoof stock, pigs, raccoons, and other mammals, without species distinction.

^dIncludes dolphins, orcas, sea lions, sharks, other fish, and other nonvenomous marine mammals.

The number of animal-encounter mentions increased 18%, from 3638 deaths by UCD to 4280 deaths by MCD; nonvenomous animal-encounter mentions increased 20%, from 2138 deaths by UCD to 2567 deaths by MCD, and venomous animal-encounter mentions increased 14%, from 1500 deaths by UCD to 1713 deaths by MCD. Of the 642 additional MCD animal-encounter mentions, the most frequently reported UCD were diseases of the heart (n = 211, 33%); infections (n = 146, 23%), including septicemia (n = 59) and potentially zoonotic infections (n = 55); malignant neoplasms (n = 44, 7%); unintentional injuries (n = 36, 6%); and cerebrovascular incidents (n = 26, 4%).

The MCD analysis revealed 429 additional nonvenomous animal-encounter mentions, predominantly other reptiles, other mammals, nonvenomous insect and other nonvenomous arthropods, and dogs (Table 1; Figure 1). Of 118 mentions of other mammals (MCD), 47 (40%) reported potential zoonotic infection for UCD, including 26 pasteurellosis, 9 septicemia, 4 rabies, and 1 tularemia. Of 77 animal-encounter mentions of dogs (MCD), 18 (23%) decedents died of potential zoonotic infection (UCD), including 12 septicemia (1 each Streptococcal and Staphylococcus aureus), 3 pasteurellosis, and 1 rabies. Of 7 animal-encounter mentions of rats, 4 decedents had a UCD of a potential zoonotic infection suggesting rat-bite fever: 2 endocarditis and 2 Streptobacillus. Animal-encounter mentions of other reptiles (nonvenomous lizards, snakes, turtles, and other unspecified reptiles) increased 2.6-fold (78 UCD, 206 MCD), surpassing mentions of marine animal encounters.

MCD analysis resulted in 213 additional mentions of venomous animal encounters, primarily hornets, wasps, bees, and venomous spiders (Table 1; Figure 1). Of 87 additional mentions of hornets, wasps, and bees, 61 (70%) were UCD-coded cardiovascular or stroke. Of 73 additional mentions of venomous spiders, 22 (30%) had infection codes for UCD.

Allergic reactions contributed to 565 of 1500 (38%) venomous animal-encounter deaths (UCD), 515 with contributing anaphylactic shock codes (T78.2): 427 hornets, wasps, and bees; 66 other specified venomous arthropods; 10 venomous snakes and lizards; 10 unspecified venomous animal or plant; 1 venomous spider; and 1 scorpion. Allergy, unspecified (T78.4) contributed to 45 UCD venomous animal-encounter deaths: 33 hornets, wasps, and bees; 11 other specified venomous arthropods; and 1 unspecified venomous animal or plant. Five deaths caused by venomous animals (UCD) had contributing angioneurotic edema (T78.3): 4 hornets, wasps, and bees; and 1 specified venomous arthropod.

On average, approximately 3 times more male than female decedents died of animal encounters (UCD; Figure 2). Deaths among males outnumbered deaths among females in every year of the study by 2- to 3-fold; annual range, 125-178 (average, 148); annual rate, 9-11 deaths per 10 million population. Among females, the number of annual deaths ranged from 40-70 (average, 54), and the rate was 2-4 deaths per 10 million population. For every nonvenomous and venomous animal-encounter category (UCD) except other reptiles (39 each), the number of deaths was higher among males than among females. For nonvenomous animal encounters, the number of deaths was 2.2 times higher among males than among females (1463 vs 675), particularly for encounters with other mammals (966 vs 348). For encounters with venomous animals, the number of deaths was 4.0-fold higher among males than among females (1198 vs 302). We found differences between males and females for encounters with hornets, wasps, and bees (872 vs 191); other specified venomous arthropods (128 vs 29); and venomous snakes and lizards (88 vs 24).

Figure 2

Number and rate of animal-encounter deaths reported on death certificates as underlying cause of death, by sex, United States, 1999-2016. Data source: Centers for Disease Control and Prevention.²⁴

Of 3638 deaths caused by animal encounters (UCD), 2923 (80.3%) occurred among adults aged >35, 269 (7.4%) among children aged ≤4, and 254 (7.0%) among adults aged 20-34 (Table 2). The highest death rates per 10 million population were among men aged 35-64 and ≥65 (27.2 each). In the MCD analysis, decedents aged ≥65 represented 358 of 642 (55.8%) additional animal-encounter mentions; overall increase, 31% (1150 UCD, 1508 MCD): nonvenomous, 36% (760 UCD, 1033 MCD) and venomous, 22% (390 UCD, 475 MCD; Tables 2 and 3).

Table 2

Underlying cause of death (UCD) animal-encounter mentions, by age, sex, race, and nonvenomous or venomous animal encounter (ICD-10 codes),^a United States, 1999-2016^b

UCD animal-encounter mentions	Total	Age group, y, no. (%)
UCD animal-encounter mentions	Total	<1	1-4	5-9	10-19	20-34	35-64	≥65
Sex
Male	2661	38 (1.4)	131 (4.9)	69 (2.6)	51 (1.9)	195 (7.3)	1345 (50.5)	832 (31.3)
Female	977	28 (2.9)	72 (7.4)	39 (4.0)	33 (3.4)	59 (6.0)	428 (43.8)	318 (32.5)
Total	3638	66 (1.8)	203 (5.6)	108 (3.0)	84 (2.3)	254 (7.0)	1773 (48.7)	1150 (31.6)
Race
White	3258	54 (1.7)	151 (4.6)	88 (2.7)	76 (2.3)	224 (6.9)	1582 (48.6)	1083 (33.2)
Black/African American	287	10 (3.5)	39 (13.6)	13 (4.5)	4 (1.4)	21 (7.3)	150 (52.3)	50 (17.4)
Asian/Pacific Islander	37	1 (2.7)	4 (10.8)	1 (2.7)	2 (5.4)	4 (10.8)	16 (43.2)	9 (24.3)
American Indian/Alaska Native	56	1 (1.8)	9 (16.1)	6 (10.7)	2 (3.6)	5 (8.9)	25 (44.6)	8 (14.3)
Total	3638	66 (1.8)	203 (5.6)	108 (3.0)	84 (2.3)	254 (7.0)	1773 (48.7)	1150 (31.6)
Animal encounter (ICD-10 code)
Nonvenomous animals
Bitten or struck by other mammals (W55)^c	1314	16 (1.2)	67 (5.1)	47 (3.6)	58 (4.4)	104 (7.9)	517 (39.3)	505 (38.4)
Bitten or struck by dog (W54)	553	46 (8.3)	119 (21.5)	53 (9.6)	8 (1.4)	19 (3.4)	158 (28.6)	150 (27.1)
Bitten or stung by nonvenomous insect and other nonvenomous arthropods (W57)	155	1 (0.6)	5 (3.2)	0	2 (1.3)	26 (16.8)	83 (53.5)	38 (24.5)
Bitten or crushed by other reptiles (W59)	78	0	1 (1.3)	0	0	3 (3.8)	15 (19.2)	59 (75.6)
Contact with marine animal (W56)^d	23	0	0	1 (4.3)	4 (17.4)	1 (4.3)	13 (56.5)	4 (17.4)
Bitten or struck by crocodile or alligator (W58)	12	0	1 (8.3)	0	0	4 (33.3)	4 (33.3)	3 (25.0)
Bitten by rat (W53)	3	0	0	0	0	0	2 (66.7)	1 (33.3)
Total nonvenomous	2138	63 (2.9)	193 (9.0)	101 (4.7)	72 (3.4)	157 (7.3)	792 (37.0)	760 (35.5)
Venomous animals
Contact with hornets, wasps, and bees (X23)	1063	1 (0.1)	2 (0.2)	1 (0.1)	4 (0.4)	59 (5.6)	711 (66.9)	285 (26.8)
Contact with other specified venomous arthropods (X25)	157	1 (0.6)	0	0	3 (1.9)	12 (7.6)	105 (66.9)	36 (22.9)
Contact with venomous spiders (X21)	124	0	1 (0.8)	3 (2.4)	2 (1.6)	9 (7.3)	78 (62.9)	31 (25.0)
Contact with venomous snakes and lizards (X20)	112	0	5 (4.5)	3 (2.7)	3 (2.7)	13 (11.6)	66 (58.9)	22 (19.6)
Contact with unspecified venomous animal or plant (X29)	31	0	0	0	0	3 (9.7)	16 (51.6)	12 (38.7)
Contact with scorpions (X22)	7	1 (14.3)	2 (28.6)	0	0	1 (14.3)	2 (28.6)	1 (14.3)
Contact with centipedes and venomous millipedes (tropical) (X24)	5	0	0	0	0	0	2 (40.0)	3 (60.0)
Contact with venomous marine animals and plants (X26)	1	0	0	0	0	0	1 (100.0)	0
Contact with other specified venomous animals (X27)	0	0	0	0	0	0	0	0
Total venomous	1500	3 (0.2)	10 (0.7)	7 (0.5)	12 (0.8)	97 (6.5)	981 (65.4)	390 (26.0)
Total animal-encounter mentions	3638	66 (1.8)	203 (5.6)	108 (3.0)	84 (2.3)	254 (7.0)	1773 (48.7)	1150 (31.6)

Abbreviation: ICD-10, International Classification of Diseases, 10th Revision.

^aData source: National Center for Health Statistics.²³

^bData source: Centers for Disease Control and Prevention.²⁴

^cIncludes cats, horses, cows, other hoof stock, pigs, raccoons, and other mammals, without species distinction.

^dIncludes dolphins, orcas, sea lions, sharks, other fish, and other nonvenomous marine mammals.

Table 3

Multiple cause of death (MCD) animal-encounter mentions, by age, sex, race, and nonvenomous or venomous animal encounter (ICD-10 code),^a United States, 1999-2016^b

MCD animal-encounter mentions	Total	Age group, y, no. (%)
MCD animal-encounter mentions	Total	<1	1-4	5-9	10-19	20-34	35-64	≥65
Sex
Male	3048	40 (1.3)	134 (4.4)	70 (2.3)	57 (1.9)	217 (7.1)	1510 (49.5)	1020 (33.5)
Female	1230	29 (2.4)	72 (5.9)	40 (3.3)	37 (3.0)	63 (5.1)	501 (40.7)	488 (39.7)
Total	4278	69 (1.6)	206 (4.8)	110 (2.6)	94 (2.2)	280 (6.5)	2011 (47.0)	1508 (35.3)
Race
White	3834	57 (1.5)	154 (4.0)	89 (2.3)	84 (2.2)	239 (6.2)	1789 (46.7)	1422 (37.1)
Black/African American	341	10 (2.9)	39 (11.4)	14 (4.1)	5 (1.5)	29 (8.5)	178 (52.2)	66 (19.4)
Asian/Pacific Islander	41	1 (2.4)	4 (9.8)	1 (2.4)	2 (4.9)	6 (14.6)	16 (39.0)	11 (26.8)
American Indian/Alaska Native	62	1 (1.6)	9 (14.5)	6 (9.7)	3 (4.8)	6 (9.7)	28 (45.2)	9 (14.5)
Total	4278	69 (1.6)	206 (4.8)	110 (2.6)	94 (2.2)	280 (6.5)	2011 (47.0)	1508 (35.3)
Animal encounter (ICD-10 code)
Nonvenomous animals
Bitten or struck by other mammals (W55)^c	1432	17 (1.2)	67 (4.7)	47 (3.3)	63 (4.4)	106 (7.4)	556 (38.8)	576 (40.2)
Bitten or struck by dog (W54)	630	46 (7.3)	119 (18.9)	54 (8.6)	8 (1.3)	22 (3.5)	189 (30.0)	192 (30.5)
Bitten or stung by nonvenomous insect and other nonvenomous arthropods (W57)	245	2 (0.8)	5 (2.0)	1 (0.4)	3 (1.2)	30 (12.2)	126 (51.4)	78 (31.8)
Bitten or crushed by other reptiles (W59)	206	1 (0.5)	1 (0.5)	0	0	3 (1.5)	29 (14.1)	172 (83.5)
Contact with marine animal (W56)^d	31	0	0	1 (3.2)	4 (12.9)	2 (6.5)	15 (48.4)	9 (29.0)
Bitten or struck by crocodile or alligator (W58)	13	0	1 (7.7)	0	0	4 (30.8)	5 (38.5)	3 (23.1)
Bitten by rat (W53)	10	0	1 (10.0)	0	1 (10.0)	0	5 (50.0)	3 (30.0)
Total nonvenomous	2567	66 (2.6)	194 (7.6)	103 (4.0)	79 (3.1)	167 (6.5)	925 (36.0)	1033 (40.2)
Venomous animals
Contact with hornets, wasps, and bees (X23)	1150	1 (0.1)	3 (0.3)	1 (0.1)	4 (0.3)	64 (5.6)	751 (65.3)	326 (28.3)
Contact with other specified venomous arthropods (X25)	180	1 (0.6)	1 (0.6)	0	3 (1.7)	12 (6.7)	114 (63.3)	49 (27.2)
Contact with venomous spiders (X21)	197	0	1 (0.5)	3 (1.5)	3 (1.5)	18 (9.1)	123 (62.4)	49 (24.9)
Contact with venomous snakes and lizards (X20)	129	0	5 (3.9)	3 (2.3)	5 (3.9)	14 (10.9)	74 (57.4)	28 (21.7)
Contact with unspecified venomous animal or plant (X29)	40	0	0	0	0	4 (10.0)	20 (50.0)	16 (40.0)
Contact with scorpions (X22)	8	1 (12.5)	2 (25.0)	0	0	1 (12.5)	2 (25.0)	2 (25.0)
Contact with centipedes and venomous millipedes (tropical) (X24)	7	0	0	0	0	0	3 (42.9)	4 (57.1)
Contact with venomous marine animals and plants (X26)	2	0	0	0	0	0	1 (50.0)	1 (50.0)
Contact with other specified venomous animals (X27)	0	0	0	0	0	0	0	0
Total venomous	1713	3 (0.2)	12 (0.7)	7 (0.4)	15 (0.9)	113 (6.6)	1088 (63.5)	475 (27.7)
Total animal-encounter mentions	4280	69 (1.6)	206 (4.8)	110 (2.6)	94 (2.2)	280 (6.5)	2013 (47.0)	1508 (35.2)

Abbreviation: ICD-10, International Classification of Diseases, 10th Revision.

^aData source: National Center for Health Statistics.²³

^bData source: Centers for Disease Control and Prevention.²⁴

^cIncludes cats, horses, cows, other hoof stock, pigs, raccoons, and other mammals, without species distinction.

^dIncludes dolphins, orcas, sea lions, sharks, other fish, and other nonvenomous marine mammals.

Of 2138 nonvenomous animal encounters (UCD), the category with the highest mortality was other mammals (n = 1314, 61.5%) followed by dogs (n = 553, 25.9%; Table 2). Among encounters with other mammals (UCD), mortality was highest among adults aged 35-64 (n = 517) and ≥65 (n = 505). Of 553 dog-encounter deaths, 165 (29.8%) occurred among children aged ≤4, 158 (28.6%) among adults aged 35-64, and 150 (27.1%) among adults aged ≥65. The MCD analysis, compared with the UCD analysis, revealed 183 additional animal-encounter mentions for other mammals and dogs (1330 vs 1513) among adults aged ≥35 (Tables 2 and 3). By age group, adults aged ≥65 had the most additional mentions for encounters with other reptiles (n = 113), other mammals (n = 71), and dogs (n = 42) in the MCD analysis as compared with the UCD analysis.

Of 1500 venomous animal-encounter deaths (UCD), 1063 (70.9%) were caused by hornets, wasps, and bees; 157 (10.5%) by other specified venomous arthropods; 124 (8.3%) by venomous spiders; and 112 (7.5%) by venomous snakes and lizards (Table 2). Of 1500 venomous animal-encounter deaths, 981 (65.4%) occurred among adults aged 35-64 and 390 (26.0%) among adults aged ≥65. Eighty-one additional mentions (MCD) occurred among decedents aged ≥35 for encounters with hornets, wasps, and bees (Table 3).

More White decedents than decedents from other racial groups had animal-encounter fatalities: 3258 of 3638 (89.6%) UCD and 576 of 642 (89.7%) additional mentions in the MCD analysis (Tables 2 and 3). Of animal-encounter fatalities with known autopsy information, autopsies were performed in 45.4% (1218 of 2683) of UCD and 39.3% (155 of 394) of additional mentions in the MCD analysis. Autopsy information was unknown for 955 of 3638 (26.2%) UCD animal encounters and 246 of 640 (38.4%) MCD additional mentions.

Discussion

We reviewed 18 years of animal-encounter fatalities (1999-2016) using CDC WONDER for UCD, consistent with previous studies.^16
-18 We also reviewed data on MCD—a novel approach—to identify animal encounters reported on death certificates as an immediate or contributing cause of death. Our findings suggest that analyzing fatalities by underlying cause alone in CDC WONDER may result in underreporting of risk and animal-encounter fatalities. We speculate that an initiating animal injury complicated by coexisting conditions (eg, heart disease, cancer, or infection) may trigger a cascade of morbid events leading to hospitalization and fatality, overshadowing the true UCD and causal chain of events for the certifier.

According to CDC,²⁶ the leading cause of death for people aged 1-44 in the United States is unintentional injury. However, fatal animal encounters account for a small percentage of injuries inflicted on humans. Not surprisingly, the UCD for 642 additional animal-encounter mentions in the MCD analysis was primarily a condition rated in the top 5 leading causes of death (2016)²⁷: diseases of the heart (33%), malignant neoplasms (7%), unintentional injuries (6%), and cerebrovascular diseases (4%). People aged ≥65 are more likely than people aged <65 to have serious coexisting conditions; the top 2 causes of death in 2017 for people aged ≥45 were heart disease and malignant neoplasms.²⁶ In our analysis, compared with adults aged <65, adults aged ≥65 were at higher risk of death from animal encounters—primarily encounters with other reptiles, other mammals, and dogs—representing more than half of additional mentions in the MCD analysis. An older person with comorbidities who is bitten by a dog and then has a cardiovascular or cerebrovascular event may have influenced prioritization of underlying cause for the certifier, with resultant misreporting of underlying cause—the dog bite. Understanding cause-of-death terminology and causal-chain sequencing is necessary for accurate death certification.^21,22

In our study, autopsies were performed in 39% of deaths coded with contributing (MCD) animal encounters. One study found that the accuracy of cause-of-death reporting could be improved if the death certificate is completed in conjunction with the postmortem examination and amended when a discrepancy exists.²⁸ Another study found that autopsy findings led to changes in the UCD for 61% of cases involved in an autopsy in 2005; 32% involved a change in the ICD-10 code.²⁹

Consistent with previous UCD studies,^16
-18 nonvenomous animal encounters, predominantly encounters with other mammals and dogs, caused most deaths. Our analysis reemphasizes the risk of fatal dog encounters among children aged ≤4. Annually, in the United States, more than 1 million emergency department visits for bites or scratch wounds are reported (about 300 000 of which are for dog bites or scratches); however, not all of these bites or scratches are associated with infections.³⁰ Of all animal bites, 3%-18% of dog bites and 28%-80% of cat bites become infected.^30
-32 Our study found that among 642 additional MCD animal-encounter mentions, infections (n = 146) ranked second for UCD, and many of the ICD-10 codes were consistent with zoonotic disease (ie, pasteurellosis, rabies, Steptobacillus, and tularemia), suggesting that an animal encounter may be the UCD and highlighting potential misclassification or misreporting UCD certification.

Limitations

This study had several limitations. First, the classification of UCD and MCD in CDC WONDER depends on the accuracy of death certification. Errors in UCD and causation sequencing may result in misclassification of ICD-10 codes and high error rates in death certification, according to multiple studies.^33

-38 Second, ICD-10 codes for animal encounters do not distinguish among species of animals, making it difficult to attribute risk to specific animals. Third, CDC WONDER data do not include death certificate information on place of injury, injury description, and injury at work, which could provide clues to underlying cause circumstances and causal sequence.

Conclusions

Our findings support a combined CDC WONDER analysis of UCD and MCD animal-encounter fatalities to accurately present animal-encounter fatality statistics and elucidate potential misreporting. Errors and misreporting of UCD certification are common and may result in inaccurate ICD-10 coding and underreporting fatality statistics. Ongoing training of medical certifiers is indicated, focusing on accurate identification of UCD and sequence of conditions leading to the final disease or condition. It is important to understand that the disease or injury that initiated the chain of events (ie, animal encounter) is reported on the death certificate as UCD to inclusively describe the risk of animal encounters through accurate fatality statistics. Fewer than half of fatalities had autopsies, which are possibly the gold standard for accuracy in death certification.

This study indicates that people of all ages are at risk of fatal animal encounters. Fatal dog encounters among children aged ≤4 are particularly concerning. Adults aged ≥65 were more likely than people aged <65 to have fatal encounters with other reptiles, other mammals, and dogs. These findings support an exploration of targeted age group–based preventive education using a One Health approach^2

-5 to nurture the human–animal bond while teaching respect for and appropriate behavior around animals. Children aged ≤4 would likely benefit from education provided to parents, caregivers, and teachers in multiple venues using a One Health approach to prevent dog bites.

Footnotes

Acknowledgments

The authors thank Kenneth D. Kochanek, MA, statistician, from the US Department of Health and Human Services, Centers for Disease Control and Prevention (CDC), National Center for Health Statistics for his expertise and insightful assistance with CDC WONDER and our research. The views contained in this article are those of the authors and do not necessarily represent the official position of CDC.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support with respect to the research, authorship and/or publication of this article.

ORCID iD

Marilyn Goss Haskell, DVM, MPH

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