Each year, Americans make more than 6 million visits to hospital emergency departments for animal-related injuries caused by creatures great (such as dogs and alligators) and small (such as snakes and spiders), according to research published Monday in the journal Trauma Surgery & Acute Care Open.

Those hospital visits cost the U.S. economy about $1.2 billion annually, the study also found.

The actual figures are probably much, much higher, however. For the study did not include emergency department visits associated with treating insect-borne illnesses, such as Lyme disease or West Nile virus. Nor did it include an assessment of non-emergency department costs, such as doctors’ fees, outpatient clinic charges, expenses related to rehabilitation, and lost productivity.

In fact, the study’s authors — a team of trauma surgeons from Stanford University — argue that if all the costs were added up, the annual burden on the U.S. economy from animal-related injuries might be more like $13 billion.

They also say that the problem will likely worsen in coming years due to climate change, which is expanding the territory where certain venomous animals can dwell, and to the increasing incursion of housing and other developments on existing animal habitats.

Types of injuries

For the study, the researchers used data submitted to the National Emergency Department Sample (NEDS) on animal-related injuries treated in emergency departments across the U.S. between 2010 and 2014.

They found that during that five-year period, 6.4 million emergency visits were made to hospitals for such injuries — a rate of 410 injuries for every 100,000 people living in the U.S.

The average age of the patients was 31 years.

Most of the injuries — 2.6 million (41 percent) — were caused by non-venomous insect or spider bites. The next-highest category of injuries — 1.6 million (26 percent) — was dog bites, followed by hornet, wasp or bee stings, which numbered 812,000 (13 percent).

The South had the greatest proportion of people (43 percent) showing up in emergency departments with animal-related injuries. The West, however, had the greatest proportion requiring treatment for bites from scorpions (87 percent) and from venomous centipedes and millipedes (83 percent).

The most common animal-related injuries treated in emergency departments in the Midwest during the study period were dog bites (350,680, or 21 percent of the total number), followed by hornet, wasp and bee bites (188,860, or 23 percent) and venomous spider bites (31,239, or 19 percent).

Midwesterners were much less likely to seek treatment for bites by venomous snakes and lizards (3,697, or 8 percent), rats (1,976, or 13 percent) or scorpions (236, or 1 percent).

The role of age and poverty

About 3 percent (210,000) of the patients in the study ended up being admitted to the hospital because of their animal-related injuries. Almost a third of them were individuals who had been stung by hornets, wasps or bees. But the injury that was most likely to end up with a hospital admission was a bite from a venomous snake or lizard. One in four people with those bites had to be hospitalized.

The researchers also found that 1,162 people died from their animal-related injuries during the study period. Although hornet, wasp or bee stings caused most (278) of the deaths, people had a higher chance of dying after bites from rats (6.5 deaths per 100,000 bites), venomous snakes and lizards (6.4 deaths per 100,000 bites) and dogs (6.1 deaths per 10,000 bites).

Both rat bites and dog bites can lead to serious and potentially life-threatening bacterial infections in humans.

Some groups were at greater risk than others. People aged 85 and older were six times more likely to be admitted to a hospital and 27 times more likely to die after an animal-related injury.

People with lower incomes were also more likely to be admitted to hospitals for their animal-related injuries. Indeed, the study found that ZIP codes with household incomes in the lowest 25th percentile had the greatest proportion (34 percent) of people injured by animals. That is likely a reflection of the quality of housing in such neighborhoods, as bites from venomous snakes, lizards and spiders tended to occur most often among people with lower household incomes.

The total cost for animal-related injuries over the five years was $5.96 billion, or an average of $1.2 billion annually. Bites from dogs, non-venomous spiders and insects, and venomous snakes and lizards accounted for 60 percent of those costs.

An expanding problem

“Injuries due to mountain lions, bears, alligators, and venomous snakes among other wild animals attract considerable media attention and are associated with dramatic morbidity and mortality,” the study’s authors write in their paper.

Yet injuries — including life-threatening ones — from smaller creatures, particularly spiders and insects, are much more numerous, they point out.

“These arthropod encounters are likely to increase based on habitat availability and climate change, and consequently may be more likely to result in a greater economic and healthcare burden than other more dramatic, but less common, animal encounters in the future,” the researchers stress.

“Understanding the burden of animal-related injuries in the USA and developing effective public health prevention measures is critical now given animal-related injuries are projected to increase,” they add.

FMI: You’ll find the study on the Trauma, Surgery & Acute Care Open website.