Caribbean chikungunya outbreak grows, poses threat to US

Health officials are reporting a sharp rise in the number of patients sickened in a chikungunya fever outbreak centered on the Caribbean island of St. Martin, which may signal an increasing risk to the US mainland.

On the French part of the island, where most of the infections have been reported, the number of confirmed cases has risen from 26 to 66, according to a Dec 28 update from the European Centre for Disease Prevention and Control (ECDC).

In addition, health officials from the Netherlands have confirmed the first case on the Dutch side of St. Martin (Sint Maarten), and illnesses have been detected on two other nearby islands: three on Martinique and one on Guadeloupe, according to the ECDC report. Both of those islands are south and slightly east of St. Martin.

The case in Guadeloupe represents the island's first documented local chikungunya case, which was detected because of enhanced surveillance for the disease in all French Caribbean territories, the ECDC said. The patient is co-infected with dengue serotype 4 and had not recently traveled to another area where chikungunya exists.

Meanwhile, health officials in the area are investigating a slew of suspected and probable cases. They include 167 suspected cases and 14 probable cases on the French side of St. Martin, and two patients have been hospitalized. Martinique has 27 suspected cases, and on the island of St. Barthelemy, 21 suspected cases are under investigation.

The outbreak represents the first known indigenous transmission of chikungunya fever in the Americas. The ECDC said in its update that the outbreak underscores the recommendations it made earlier this month, urging health providers to heighten their vigilance against the disease, especially with increased travel during the holidays.

Chikungunya is a viral disease spread mainly by Aedes aegypti and A albopictus mosquitoes. When symptomatic, it typically causes fever and arthralgia, similar to dengue.

The outbreak in the Caribbean recently prompted two alerts from the US Centers for Disease Control and Prevention (CDC)—a Health Alert Network (HAN) notice to health providers and an advisory to travelers.

Steps to minimize US threat

Erin Staples, MD, PhD, a medical epidemiologist with the CDC's National Center for Emerging and Zoonotic Infectious Diseases in Fort Collins, Colo., told CIDRAP News that health officials are concerned that the chikungunya virus could gain a US foothold. Infected travelers who return home to the United States can introduce the virus into local A aegypti and A albopictus populations when bitten by the mosquitoes.

It's impossible to predict how the disease could spread in the United States, but there's a chance health officials could see small, focal outbreaks, similar to small pockets of dengue fever infections that have been detected in areas such as those near Miami, she said. "We're looking at this closely and staying on top of this."

The arrival of chikungunya fever in temperate areas of Europe in 2007 was a wake-up call that the virus could also surface in the United States, and the CDC has strengthened the ability of labs to detect the disease and has developed resources to allow clinicians to diagnose infections in patients, Staples said.

She said two key strategies for minimizing the threat to the United States are to encourage travelers to wear insect repellent and take other precautions against mosquitoes and to boost awareness among health providers so that they can recognize the disease early, which could curb virus transmission to local mosquitoes. Vector control at mosquito breeding sites is another important tool, Staples added.

See also:

Dec 28 ECDC weekly communicable disease threat report

Dec 13 CDC travel notice

Dec 13 CDC HAN advisory

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