Locally Acquired Dengue Case Confirmed in California

A case of locally acquired dengue fever has been confirmed in a resident of Baldwin Park, California, according to a press release from the Los Angeles County Department of Public Health. This locally acquired case of dengue is the third to be reported in California and the first to be reported by the Los Angeles County Department of Public Health; cases were confirmed in Pasadena and Long Beach, California, in the fall of 2023.

“Dengue is the most common insect-borne viral infection in the world, with a wide geographic spread; we know that we have mosquitos capable of carrying and transmitting the virus in the United States already, and Los Angeles county is a major epicenter for international travel and trade,” said James Lawler, MD, associate director for International Programs and Innovation at the Global Center for Health Security and professor in the Infectious Diseases Division at the University of Nebraska Medical Center, Omaha, Nebraska, in an interview.

Although the patient had no known history of travel to a dengue-endemic area, the potential risk for widespread transmission of the virus in the Los Angeles County area remains low, and no additional suspected cases of locally acquired dengue have been identified, according to the release. However, the recent cases highlight the need for vigilance on the part of the public to reduce transmission of mosquito-borne infections, the public health department noted.

Most cases of dengue occur in people who have traveled to areas where the disease is more common, mainly tropical and subtropical areas, according to the press release. However, the types of mosquitoes that spread dengue exist in parts of the United States, so locally acquired infections can occur.

The Centers for Disease Control and Prevention (CDC) issued an official health advisory in June 2024 about an increased risk for dengue infections in the United States. According to the advisory, 745 cases of dengue were identified in US travelers to endemic areas between January 1, 2024, and June 24, 2024.

The CDC advises clinicians to maintain a high level of suspicion for dengue among individuals with fever and recent travel to areas with frequent dengue transmission, but also to consider locally acquired disease in areas of mosquito vectors.

In clinical practice, dengue may be difficult to differentiate from other febrile systemic infections, Lawler noted. “Joint pain, low back pain, and headache (often retro-orbital) are common and can be severe, and a rash often appears several days into illness,” he noted.

Do not delay treatment in suspected cases while waiting for test results, the CDC emphasized in the advisory. Food and Drug Administration–approved tests for dengue include RT-PCR and IgM antibody tests or NS1 and IgM antibody tests.

“Severe dengue can be life-threatening and progress to a hemorrhagic fever-like syndrome, and patients with severe dengue should be cared for on a high-acuity or intensive care setting, with close monitoring of labs and fluid status,” Lawler told Medscape Medical News.

The World Health Organization has published guidelines for the management of dengue, which Lawler strongly recommends to clinicians in the rare event that they are facing a severe case. The treatment for dengue is supportive care, according to the CDC; a vaccine that was deemed safe and effective is no longer being manufactured because of low demand.

Most symptoms last for 2-7 days, and most patients recover within a week, but approximately 1 in 20 may develop severe disease, according to the Los Angeles County Department of Public Health.

Approximately one quarter of dengue infections are symptomatic, and clinicians should know the signs of progression to severe disease, which include abdominal pain or tenderness, persistent vomiting, clinical fluid accumulation, mucosal bleeding, lethargy or restlessness, and liver enlargement, according to the CDC.

Local Dengue Not Unexpected

“Sadly, I am not surprised at another locally acquired case of dengue fever in the United States,” said Lawler. “We also have seen a trend of more historically tropical, insect-borne diseases popping up with locally acquired cases in the United States,” he noted.

Lawler suggested that “the erosion of state and local public health” is a major contributor to the increase in dengue cases. For more than 100 years, activities of state and local public health officials had significantly curtailed mosquito-borne diseases through aggressive control programs, “but we seem to be losing ground over the last several years,” he told Medscape Medical News.

“Locally acquired dengue cases are still rare in the United States,” Lawler told Medscape Medical News. “However, people can protect themselves against dengue and more common arthropod-borne infections by taking precautions to cover up and wear insect repellent while outdoors,” he said.

In addition, the Los Angeles County Department of Public Health emphasized in its press release that local residents reduce their risk for contact with mosquitoes by removing areas of standing water on their property and ensuring well-fitted screens on doors and windows.

Lawler had no financial conflicts to disclose.