Discussion
Venomous snakebites are an important public health issue in the USA, possibly occurring more frequently than previously described. We identified more than 11 000 patients treated for venomous snakebites in the USA in 2016, a quantity approximately 2.5 times larger than the number of venomous snakebites in the USA in 2016 reported by the AAPCC.7 Existing research using national injury registries reported even fewer venomous snakebites, with annual averages ranging from 2825 to 3188.2 5 These discrepant results illustrate limitations of registries dependent on passive surveillance and highlight the need to perform a comprehensive national assessment using NEDS.
The NEDS data enable us to characterize the epidemiology of venomous snakebites in the USA and challenge the validity of the “T’s of snakebites” at the national level. Having never been rigorously evaluated, the “T’s of snakebites” originate from anecdotes used to humorously highlight colloquial risk factors for venomous snakebites. These risk factors include testosterone, teasing, touching, trucks, tattoos & toothless (poverTy), Texas, tequila, teenagers, and tanks (vivarium) (online supplementary file).
Testosterone: “maleness”
Male sex has been described as a risk factor for venomous snakebites among regional and national reports, with 69% to 80% of snakebite victims having been reported as male.2–4 13 20–23 Our study found that 65% of snakebite victims were male. There are several potential explanations. First, existing studies have used data which may be subject to selection bias inherent to smaller locoregional sample sizes. Another possible explanation is a change in demographics over time. However, previous studies describing the sex distribution of venomous snakebite victims vary considerably, suggesting changing demographics are not responsible. Ultimately, irrespective of the differences between NEDS and previously reported data, males more commonly present with venomous snakebites than females.
Teasing and Touching: intentional interaction
Among patients in the NEDS data set, 50% of snakebite victims were bit in the upper extremity, with 44% snakebites affecting the wrist, hand, and fingers. These upper extremity snakebites may represent encounters where the person was attempting to touch or grasp the snake. In studies that have examined snakebites incurred through intentional contact, more than 90% of victims were males and almost all were associated with upper extremity snakebites.2–4 12 21 24 Unfortunately, NEDS does not capture intentionality at a detailed enough level to assess whether a venomous snakebite victim was trying to touch or grasp a snake versus inadvertently having his or her hand in close proximity to a venomous snake. Other injury registries differentiate intention based on whether the victim saw the snake and could have avoided the encounter.25 The only intentional acts captured in NEDS are injuries caused by intentional self-harm or assault. Overall, the large number of snakebites that occur on the hands and distal upper extremity suggest that teasing and touching may be reasonable risk factors for venomous snakebites.
Trucks: “ruralness”
“Trucks” suggests that living in rural areas is a risk factor for venomous snakebites. While 19% of the US population lives in a rural county, we found that 34% of snakebite victims presented to a hospital in a rural county, suggesting that venomous snakebites may be more common in rural areas.26 However, more than double the number of patients presents to non-rural-county EDs than rural-county EDs. There are several possible explanations. First, because most snakebites are not immediately lethal, a rural snakebite victim may travel to a suburban or urban area to receive medical treatment. Second, patients may seek care from larger, urban academic medical centers believing they offer more advanced clinical capabilities.27–30 A third explanation is that human expansion and snake habitat loss may put humans in traditionally non-rural areas in closer proximity to venomous snakes.31–33 Snakes may seek shelter and prey in barns, garages, sheds, gardens, and wood or dirt piles; prior studies have reported that most snakebites occur within 1.61 kilometers (one mile) of the home.34 So although being in a rural area appears to be associated with a disproportionate number of ED presentations for venomous snakebites, this risk factor may change over time. Using “trucks” as a proxy for “ruralness” does not adequately capture the epidemiology of venomous snakebite injury and does not adequately reflect the rural–suburban–urban distribution of venomous snakebite injury.
poverTy: socioeconomic status
The colloquial “T’s” of “tattoos” and “toothless” are offensive terms historically used as descriptors for risk factors for snake envenomation. As neither of the prior terms are able to be analyzed in NEDS, we elected to use “poverTy” as a substitute. Socioeconomic statuses of snakebite victims have rarely been characterized.35 We found that most snakebite victims (39%) were in the lowest quartile for household income compared with zip code, validating that lower socioeconomic status may be a risk factor for venomous snakebites. Supporting this finding, a prior study of institutional-level venomous snakebite data found that only 29% of snakebite victims were employed.35 We found 20% of venomous snakebite victims were on Medicaid, similar to the 19% of the USA enrolled in Medicaid, suggesting that being on Medicaid is not a risk factor.36 However, 18% of snakebite victims in NEDS were self-pay or uninsured, compared with only 8% of the general US population.36 The higher frequency of patients in the lowest income quartile and uninsured patients lends credence to the “T’s” suggesting increased risk with lower socioeconomic status.
A strong interrelationship exists between socioeconomic status and race. Few prior studies comment on the race of snakebite victims. In a study from 1966, the weighted incidence of snakebites per 100 000 population was estimated as 4.99 for white males, 5.87 for non-white males, 2.44 for white females, and 2.48 for non-white females.37 In the same study, whites had higher venomous snakebite rates than non-whites in 42 of 50 (84%) states. Unfortunately, NEDS does not report race data. However, among patients admitted after a venomous snakebite in the National Inpatient Sample, 84% were white (2019 Forrester JD, unpublished data).38 The same year, 73% of the US population were white.39 Therefore, the colloquial terms used to describe risk associated with white patients belonging to lower socioeconomic classes may be valid.
Texas: geography
Venomous snakes are more common in the warmer climates of the southwestern, southern, and southeastern USA.1 16 37 An analysis of 20 years of National Vital Statistics System data found three southern states—Texas, Florida, and Georgia—accounted for 44% of venomous snakebite deaths in the USA.2 40 In a pediatric snakebite registry review, most cases were reported in Texas, Florida, Georgia, North Carolina, Arizona, and California.41 Concordantly, our data indicate that 82% of snakebites occurred in the South, 11% in the West, 7% in the Midwest, and 1% in the Northeast. Although Texas appears to be an accurate term to describe venomous snakebite risk, the term does not capture the broader risk associated with being in the southern and western USA.
Tequila: alcohol consumption
Alcohol consumption may be a risk factor for snake envenomations.14 Existing literature has reported variable proportions of snakebites related to alcohol consumption, with findings ranging from 1% to 64%.13 14 21 42–44 A recent report of US poison control data reported that only 1% of snakebites were associated with alcohol or drug use.31 Unfortunately, NEDS has limited alcohol and drug use data, so no national-level estimates are provided. Further research is needed to determine if “tequila” is an appropriate moniker to describe the frequency of drug and alcohol use among venomous snakebite victims.
Teenagers: age
Age-specific venomous snakebite rates are valuable when targeting prevention efforts. In 1966, 52% of snakebites were reported among individuals younger than 20 years old, with a rate of 6 snakebites per 100 000 population for children and teenagers aged 5 to 19.37 Existing research concluded that 28% of snakebites affected children less than 12 years old, and that children 0 to 14 years old and 15 to 19 years old accounted for 22% and 9% of all snakebites, respectively.2 4 Our study found that 22% of snakebite victims were aged 0 to 17. However, after age-adjusting the NEDS data using the 2016 US population, patients aged 0 to 17 had lower odds of venomous snakebite, and the greatest odds were seen among patients 45 to 64 years old. Unfortunately, this may be confounded by outdoor recreational activities that inadvertently expose persons to venomous snakes; it is not known which activities are more likely to put a person at risk and which age groups are more likely to be participating in these activities.45 Broadly speaking, teenagers do not appear to be at increased risk for venomous snakebite injury; “teenagers” may be an inappropriate “T.”
Age correlated with snakebite location.12 In our study, we found that 63% of snakebites in individuals 0 to 17 years old affected the lower extremities, whereas 58% of snakebites affected the upper extremities in individuals >18 years old. Similarly, among children 0 to 10 years of age, prior studies report the lower extremity as the most common snakebite site, with 75% of snakebites affecting the leg, ankle, and foot.10 The differences in snakebite location based on age question the role of intentionality; it is possible that children are less likely to be bitten by a venomous snake while intentionally trying to grasp the reptile. Instead, children may unintentionally walk near a venomous snake and fail to notice the presence of the reptile or fail to recognize the signs of an impending snakebite. This may represent an opportunity for public health intervention.
Tanks: pets and exotic snake species
We found that a small fraction of injuries are caused by exotic snakes, consistent with existing literature.6–8 Exotic snakes are becoming increasingly popular pets in the USA, whether legally or illegally.9 Most exotic snakebites affect individuals employed at zoos or pet stores or owners of private collections.16 From 1995 to 2004, the Toxic Exposure Surveillance System database of the AAPCC recorded envenomation by 77 species of exotic snakes, averaging 39.9 per year with a total of three fatalities.9 20 We identified only 34 exotic snakebites in 2016, with the cobra species the most common exotic venomous snake responsible for biting humans, similar to prior assessments.34 However, without a denominator of the number of persons possessing exotic venomous snakes, attribution of increased risk is not possible.
Limitations
There are several limitations to this study. First, only snakebite victims in the USA were analyzed, limiting extrapolation to other countries. Second, misclassification bias may exist in the ICD-10 coding, as the validity of the coding is dependent on the quality of the coder. Third, the large number of unidentified snakes could lead to over-representation or under-representation of certain snake species. Fourth, NEDS only collects event-level data without unique identifiers for individual patients, meaning that a person bit twice during the course of 1 year would be categorized as two separate patients rather than a repeat encounter. Fifth, reporting bias may affect procedural code capture; not all patients had procedural codes reported. Sixth, 81% of snakebites were not identified at a species level. Finally, although NEDS is the most comprehensive survey of ED visits in the USA, sampling error and regional variability of snake species may lead to an overestimation or underestimation of snakebites.
