Abstract
Objective
The purpose of this institutional review board-approved, cross-sectional study was to identify residual symptoms and signs of envenomation reported by snakebite survivors via a telephone survey.
Methods
Victims of rattlesnake bite who were treated at a single hospital center during a 10-year period were contacted through a telephone survey. Study subjects were included through a diagnosis-based retrospective chart review of snakebite victims, and excluded if they did not receive rattlesnake antivenom. Data collection was done using a standardized form that included sections about residual, recurrent, or new pain, weakness, paresthesias, or other limitations of the bitten limb.
Results
We identified 46 snakebite cases including 5 of 46 “dry” bites. The remaining cases (41 of 46) all received Crofab. Interviews were completed for 31% of these patients (13 of 41), and the remainder were lost to follow-up. Most bites occurred in men (12 cases, 92% males) and on the arms (9 cases, 69%). Six of the 13 respondents (46%) reported residual symptoms from the bite. Persistent symptoms described included localized pain at the bite site (3 cases), numbness or paresthesias (2 cases), abnormal skin peeling and discoloration at the bite site (2 cases), and persistent weakness of the bitten extremity (1 case). Among patients reporting persistent symptoms, the bite-to-survey interval ranged from 7 months to 12 years, with a median interval of 4 years.
Conclusions
Our study population demonstrated a notable incidence (43%) of self-reported persistent symptoms related to their rattlesnake bites, although the overall level of disability from these injuries seems low.
Keywords
Introduction
In the United States, snakebites are a commonly encountered form of environmental trauma with approximately 10,000 bites annually presenting to emergency departments. 1 The majority (98%) of venomous snakebites, at an estimated incidence of 4500 envenomations per year, arise from the family Crotalinae. 1 Although there are 10 different kinds of rattlesnakes found in California (7 species, 2 of which have subspecies), the predominant species found in the great central valley of California is Crotalus oreganus, the Northern Pacific Rattlesnake. 2
Many published reports focus on the management of venomous snakebite or the short-term morbidity related to such injuries. Long-term sequelae related to snakebite are less well defined in the literature. A study conducted by Cowin et al 3 found that patient-reported sequelae at 1 to 3 years after snakebite ranged from 30% to 70%. After a detailed review of the relevant literature, it appears that our report may be the first and only one available outlining long-term complications of snakebite. Our aim was to identify residual symptoms and signs of envenomation reported by snakebite survivors via a telephone survey in central California by performing a 10-year retrospective review of envenomation cases presenting to a tertiary-care, level-1 trauma center.
Methods
Data collection and study design were approved by the authors’ institutional review board. A retrospective chart review of victims of rattlesnake bite who were treated at our medical center during the 10-year period was performed, and these patients were subsequently contacted through a telephone survey.
Study Site And Patient Population
The study population consisted of all snakebite victims seen and treated with a crotaline antivenom, during the study period of 2000 to 2010, at our tertiary-care medical center. Dry or minor bites were excluded as they could have been caused by a misidentified snake (ie, gopher snake), and this study aimed to focus on the long-term complications of crotaline envenomation. Subjects were excluded if they did not receive rattlesnake antivenom, or sustained snakebites by nonvenomous or non-Crotalinae species.
Retrospective Data Collection
For the chart review, patients were identified using 2 methods to ensure all study subjects would be included over a period during which written records were replaced by electronic recordkeeping systems. First, all snakebite victims were identified by review of medical records using the International Classification of Diseases, Ninth Revision (ICD-9) codes E905.0 (“venomous snake and lizard bites”) and 989.5 (“toxic effect of venom”) between 2000 and 2010. Secondly, our electronic pharmacy database was queried to identify all cases in which antivenom was dispensed in the emergency department. The investigators analyzed each chart to ensure the accuracy and completeness of these diagnostic codes, as well as to eliminate redundancy in patient selection using these search methods.
All cases were deidentified, and patients were assigned a unique numerical identifier to protect identity for initial chart review. Data abstracted included patient age, sex, comorbid conditions, serum laboratory values, total doses of antivenom, and length of hospital stay. Antivenom was provided based on the treating provider’s judgment regarding the presence of significant envenomation or a coagulopathy of clinical concern. A grading system was not consistently used or documented by providers. The trends and results of this chart review have been previously published. 4
Telephone Survey
The investigators were blinded to the historical details of each patient’s care when performing the interview, for which they were given only name and contact telephone information. If patients verbally consented to the telephone questionnaire, survey data collection was done using a standardized form, which included sections about residual, recurrent, or new pain, weakness, paresthesias, or other limitations of the bitten limb (Table). Spanish-language speakers were interviewed by a native Spanish speaker. The only languages encountered were English and Spanish.
Snakebite long-term disability telephone questionnaire
Results
There were 46 snakebite cases admitted during the study period. All cases were from crotaline envenomations from wild snakes. The species is presumably C oreganus, given the natural ranges of rattlesnake species found in California. 2 Of the 46 cases, 5 were dry bites, and the remaining cases (41 of 46) all received Crofab antivenom based on the treating provider’s judgment. This correlated to a dry bite rate of 11% in the study population. Overall, there was both a male (83%) and an adult (90%) predominance, with only 4 pediatric patients (ages 4, 10, 17, and 17 years). Upper-extremity bites were more common, comprising more than three fourths of all bites (32 of 41 upper vs 10 of 42 lower extremity). One patient sustained bilateral bites to the hands. There was no sex difference in the proportion of bites to the upper extremities (females sustained bites 5 of 7 (71%) to the upper extremities, males sustained a similar proportion 26 of 35 (74%) to the upper extremities). There were no surgical interventions in our study group.
Interviews were completed for 32% of these patients (13 of 41), and the remainder were lost to follow-up. Six of the 13 respondents (46%) reported residual symptoms from the bite. Persistent symptoms described included localized pain at the bite site (3 cases), numbness or paresthesias (2 cases), abnormal skin peeling and discoloration at the bite site (2 cases), and persistent weakness of the bitten extremity (1 case). None of the study participants had any prior history of diabetes or stroke. All the participants attributed their symptoms to the sequelae of the snakebite.
Among patients reporting persistent symptoms, the bite-to-survey interval ranged from 7 months to 12 years, with a median interval of 4 years. Despite reporting persistent symptoms, there were no delays in returning to work and otherwise performing all activities of daily living that were attributable to the bite for any patients interviewed.
Discussion
Snakebite victims may experience persistent disability after these injuries. 5 Longitudinal investigations on victims of envenoming rattlesnake bites are warranted to better treat this population and provide accurate anticipatory guidance on the resolution of their injury. The present study provides some additional insights into the long-term course and persistent complications associated with crotaline envenomations in central California.
Although 46% of patients (6 of 13) who responded to our telephone-based survey reported residual symptoms, the overall level of disability from these injuries was low in our study cohort. Most patients reported an immediate ability to return to previous employment, as well as other activities of daily living or hobbies requiring manual dexterity (such as playing guitar). Furthermore, they denied activity-limiting muscle weakness. In comparison to other regional demographic studies of rattlesnake bite victims, our patient demographics and outcomes are similar to previously published work. Additionally, our patient follow-up to telephone interview (32%) matches the response rate seen in other similar questionnaire-based studies. Some of our responding patients described symptoms of paresthesias, fatigue-related pain, and sensory deficits in the areas related to the bite site, which may reflect posttraumatic syndromes such as those sometimes labeled reflex sympathetic dystrophy or complex regional pain syndrome. Future studies featuring serial physical investigations, and physiologic testing of snakebite patients in the outpatient setting, could confirm or rule out these syndromic diagnoses, which currently have unclear pathophysiology.
A 1998 study by Cowin et al 3 demonstrated a long-term complication rate of 30% for patients seen in an outpatient setting and 70% for those interviewed by telephone. The most common complications endorsed were persistent pain, weakness, or atrophy at the bite site. Cowin et al 3 reported only 1 (of 14) patients evaluated in a follow-up clinic had residual motor deficits in the upper-extremity examination, and this was attributed to a fasciotomy procedure performed on that patient. This prior study only evaluated bites to the upper extremity, however, and did not distinguish long-term complication rates according to species of snake, degree of envenomation, or use of antivenom.
Limitations
The most identifiable limitations in our study were its retrospective design and low rates of follow-up. All the patients who were selected for telephone interview were determined at the time of hospital presentation to have snakebite injury of significant severity to warrant antivenom administration, which may have biased our selection to a more severe cohort of patients. Only one-third of the patients in the study successfully completed the telephone interview, a rate that was mostly attributable to outdated contact information in the medical records. This is similar to the rates of patient telephone interview follow-up in other studies. 6 The history and identification of the snake are obtained from the chart as documented by the original provider, which is not always reliable because numerous charts were fraught with unclear details. The use of telephone interview and self-reporting of symptoms did not allow us to personally examine and test the patients for residual dysfunction in the bitten limb. Although our study focused on the physical sequelae of rattlesnake envenomation, there is still a gap in the literature regarding the psychosocial risks and sequelae of envenoming that should be addressed in future studies.
Conclusions
In central California, crotaline envenomations occurred mainly in adult males. As previously reported, dry bites or bites not requiring antivenom administration were uncommon, comprising only 10% of bites in this study population. Our study population demonstrated a notable incidence (43%) of self-reported persistent symptoms related to their rattlesnake bites, although the overall level of disability from these injuries was relatively low. Further research on snakebite survivors, exploring the pathophysiologic basis of persistent symptoms and their natural history, as well as rates of long-term disability, is strongly recommended.