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GAVIN NEWSOM
Governor

State of California—Health and Human Services Agency
California Department of Public Health


​​​​​​​​​​​​​​​​                                                            Health Advisory                                                            

TO: Healthcare Providers
Dengue Infection in California
10/30/2023



​Key Messages 

  • The first locally acquired case of dengue in California has been detected in a Pasadena resident; no other locally acquired dengue cases have been identified in California.  
  • To date, local vector control agency surveys have not identified dengue-infected mosquitoes in Los Angeles County.  
  • The potential risk for acquiring dengue virus in Los Angeles County and California remains low. 
  • Healthcare providers should consider dengue in any patient with a history of international travel and an acute febrile illness and other symptoms compatible with dengue.  
  • Providers should consider dengue in a patient without travel history if presenting with an acute febrile illness and strongly suggestive symptoms including eye pain, muscle paint, joint pain, bone pain, clinically consistent rash, nausea, and vomiting. 
  • Providers should report any dengue virus infection to local public health within one working day from identification. 

Back​ground 

The California Department of Public Health (CDPH), in collaboration with the Pasadena Public Health Department and Los Angeles County Department of Public Health, has confirmed a case of dengue in a resident of Pasadena (Los Angeles County) who did not travel outside the county before illness onset. This is the first documented case of locally acquired dengue in California; no other locally acquired dengue cases have been identified in Los Angeles County or elsewhere in California at this time. CDPH is working with local health departments and local vector control agencies to monitor for dengue cases and manage the mosquito vectors that may carry dengue viruses. The potential risk for acquiring dengue virus in Los Angeles County and California remains low. This Health Alert summarizes the current situation and provides recommendations for healthcare providers and local health jurisdictions for considering dengue and other possible mosquito-borne diseases in patients with an acute febrile illness and compatible symptoms after international travel or occasionally even without a travel history.

Situati​on 

The California Department of Public Health (CDPH), in collaboration with the Pasadena Public Health Department (PPHD) and Los Angeles County Department of Public Health (LACDPH), has recently confirmed dengue infection in a Pasadena resident with no history of domestic or international travel before onset of illness. The resident developed symptoms in mid-September 2023 and is recovering. Their household members are asymptomatic and report no history of travel.  The source of the patient’s infection is unknown at this time but is under investigation. 

No other locally acquired dengue cases have been identified in Los Angeles County or elsewhere in California at this time. The risk of local transmission of dengue in Los Angeles County and the state remains low. While the Aedes mosquitoes that can carry dengue viruses are found throughout Los Angeles County and in other California counties, no dengue-infected mosquitoes have been identified, including in the area around the patient’s residence. Local public health and vector control agencies are working together to minimize the possible risk of spread of dengue and other mosquito-borne diseases. 

From 2018 to 2022, CDPH has documented an average of 124 travel-associated cases of dengue per year among California residents. This is the first documented case of locally acquired dengue in California. Sporadic clusters and locally acquired cases of dengue have occurred in other states including in Arizona, Florida, Hawaii, and Texas. The size of clusters in these states as been relatively small and limited.  

Dengue Over​view 

Dengue is an infection in a person with any of the 4 single-stranded RNA viruses of the genus Flavivirus, dengue virus, 1,2,3, or 4 (DENV1-4). Dengue is endemic in many tropical and subtropical regions worldwide, and is primarily transmitted to humans through the bite of an infected Aedes mosquito.   

Clinical Presentation  

Dengue can range from asymptomatic infection or mild illness to severe disease. The typical incubation period is 5-7 days. Approximately one in four infected persons develop symptoms and most commonly have a mild to moderate, nonspecific, acute febrile illness. Typical clinical presentation includes acute onset of fever accompanied by a combination of the following: headache, retro-orbital pain, myalgia, bone pain, arthralgia, nausea and vomiting, macular or maculopapular rash, a positive tourniquet test, and leukopenia.  

Approximately one in twenty patients develops life-threatening disease called severe dengue. People with a prior history of dengue infection are at increased risk of severe dengue as are infants, older adults, pregnant women, and those with chronic medical conditions such as diabetes and chronic renal disease. Warning signs include abdominal pain or tenderness, persistent vomiting, mucosal bleeding, liver enlargement, clinical fluid accumulation, or laboratory results indicating an increase in hematocrit concurrent with a rapid decrease in platelets.  

For more details see CDC Clinical Presentation. ​

Prevention 

Preventing mosquito bites is the best way to prevent dengue and other mosquito-borne diseases. While there is a dengue vaccine available, it is only approved for persons with a history of laboratory-confirmed dengue infection (see CDC Dengue Vaccine). 

Aedes mosquitoes bite during the day and night and live indoors and outdoors. Information for the public, including print resources are available on the CDPH and CDC Prevent Mosquito Bites webpages.   

Persons having problems with mosquitoes in their house can be referred to their local vector control district to report problems and request assistance. See the West Nile page to locate California vector control agencies based on zip code.   

Recommendations ​

Recommendations for Healthcare Providers ​

  • Obtain a travel history in all patients presenting with acute febrile illness. 
  • Consider dengue (and other arbovirus infections) in any patient with a history of international travel and an acute febrile illness and other symptoms compatible with dengue (see Dengue Overview below).  
  • Consider dengue in a patient without travel history if presenting with an acute febrile illness and strongly suggestive symptoms including eye pain, muscle paint, joint pain, bone pain, macular or maculopapular rash, nausea, and vomiting. 
  • Obtain diagnostic tests in suspect cases. The appropriate tests depend on time since illness onset (see Laboratory Testing below).
Reporting  

Report any dengue virus infection to the local public health department by email, fax, phone, or mail within 1 working day from identification.

Laboratory Testing  

For patients presenting in the first seven days following illness onset, diagnostic testing should include both a nucleic acid amplification test (NAAT) such as real-time reverse transcription PCR (RT-PCR) and an IgM antibody test. Dengue virus antigen testing with nonstructural protein 1 (NS1 tests) can also be used to confirm infection. 

For patients presenting more than seven days after illness onset, only IgM testing is recommended. If in doubt about the timing of symptom onset, both NAAT and IgM should be ordered.   

IgG antibody tests are not useful for acute diagnosis because IgG remains detectable for life indicating long-term immunity. A limitation of serological tests is that they can cross react with other arboviruses. 

Laboratory testing is available at both commercial and public health laboratories, although some specialized laboratory tests are not widely available. Providers can contact their local public health department for guidance on laboratory testing in their jurisdiction. 

For patients suspected to have dengue, it is important to rule out infections with other arboviruses, such as West Nile virus and chikungunya virus. ​

Treatment 

No specific antiviral treatment for dengue is available.  

Patients with mild symptoms should be advised to stay well hydrated and avoid aspirin (acetylsalicylic acid), aspirin-containing drugs, and other nonsteroidal anti-inflammatory drugs (such as ibuprofen) because of their anticoagulant properties. Fever should be controlled with acetaminophen and tepid sponge baths. For at least one week, patients should use insect repellent to prevent mosquito bites and reduce the chance of further virus transmission.   

Patients with severe disease require hospitalization. 
Intravenous fluid therapy is the mainstay of supportive care. Close observation and frequent monitoring in an intensive care unit may be required. Recognizing early signs of shock and promptly initiating intensive supportive therapy can reduce risk of death among patients with severe dengue to <0.5%. Prophylactic platelet transfusions and steroids are not recommended. 

See CDC Treatment for more details.  ​

Additional Resour​ces 

CDPH​

CDC