Experts worry dengue outbreak in Puerto Rico could escalate

January 2008

PHILADELPHIA – The 2007 island-wide outbreak of dengue fever in Puerto Rico could potentially escalate to a more significant public health problem, according to experts. Public health officials warn that there is potential for a major outbreak because all four serotypes of dengue fever have been documented in Puerto Rico since January 2007.

Between January and October 2007, 7,824 cases of suspected dengue fever were reported to the Puerto Rico Department of Public Health; 2,301 of these cases were confirmed positive for dengue fever in laboratories.

“We are seeing a resurgence of dengue virus serotypes 1 and 4 and a persistence of serotypes 2 and 3,” Kay Tomashek, MD, medical officer for the CDC in San Juan, Puerto Rico, told Infectious Disease News. Tomashek presented information about the dengue fever outbreak in Puerto Rico at The 56th Annual Meeting of the American Society of Tropical Medicine and Hygiene, held recently in Philadelphia.

Tomashek said public health officials are particularly concerned about the resurgence of dengue virus serotype 1, since it has been detected for the first time in eight years.

Tomashek said although dengue fever serotypes 2 and 3 continue to account for the majority of cases, the emergence and spread of the other forms is somewhat concerning.

Dengue fever serotype 3 accounted for 61.8% of all laboratory-confirmed cases; 32.1% of the cases were confirmed as dengue fever serotype 2. Dengue fever serotype 4 accounted for 5.1% of the cases; 1% of cases were dengue fever serotype 1.

Symptoms

The principal symptoms of dengue fever are acute high fever with two or more of the following: severe headache, pain behind the eyes, muscle aches/pain, joint pains, rash, evidence of bleeding and low white cell count. Patients with dengue infection, especially children, may also present with nausea and vomiting.

There are no differences in symptoms between the four serotypes. “Each serotype is capable of causing the full spectrum of clinical disease, from asymptomatic infection to dengue hemorrhagic fever and dengue shock syndrome,” Tomashek said. “The WHO case definition for dengue is the same regardless of the infecting serotype.”

Atypical outbreak

Dengue is spread to humans by the bite of an infected mosquito and is endemic to Puerto Rico. However, according to Tomashek, transmission of dengue fever typically occurs in a seasonal pattern with minimal occurrence from March to June and a transmission peak from September to November. “But in 2007, the outbreak officially began and was declared the last week of May,” Tomashek said. “At that time only dengue virus serotypes 3 and 2 were being detected on the island. Within two months, all four serotypes were detected.”

Preventing the spread

Tomashek said health care providers and public health officials should encourage people to take steps to prevent the spread of dengue fever. “The emphasis for dengue prevention is on sustainable, community-based, integrated mosquito control, with limited reliance on insecticides,” Tomashek said. “Preventing epidemic disease requires a coordinated community effort to increase awareness about dengue, how to recognize it and how to control the mosquito that transmits it. Residents need to take responsibility for keeping their yards and patios free of sites where mosquitoes lay their eggs, primarily artificial containers that hold water. Pet and animal watering containers and vases with fresh flowers should be emptied and washed at least once a week. Residents can also protect themselves by wearing long pants and long sleeves and using an effective mosquito repellent such as those that contain DEET, picaridin or oil of lemon eucalyptus.”

For more information:

• Tomashek K, Rivera A, Hunsperger E, et al. Update on the 2007 Dengue outbreak in Puerto Rico involving all four serotypes. Presented at: The 56th Annual Meeting of the American Society of Tropical Medicine and Hygiene; Nov. 4-8, 2007; Philadelphia.