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Local transmission common during 2013 Texan dengue outbreak
A 2013 dengue outbreak in southern Texas that occurred concurrently with a nearby Mexican epidemic resulted in 53 confirmed cases of illness, of whom 55% required hospitalization, according to findings from a recently published investigation.
Furthermore, the data suggested approximately half of these confirmed cases had no recent history of travel, thus marking the largest number of locally acquired infections in a single outbreak since 1980, when dengue re-emerged in Texas.
Hospitalization rates greater than those of endemic countries
In July 2013 — the peak of a dengue epidemic in the Mexican state of Tamaulipas with more than 5,500 reported cases — the Texas Department of State Health Services received the first report of a lab-confirmed dengue case, Dana L. Thomas, MD, epidemiology field officer of the San Juan, Puerto Rico, branch of the CDC, and colleagues wrote.
Figure 1. A female Aedes aegypti mosquito, one of the primary vectors of dengue, as it feeds on human blood.
Source: James Gathany, CDC
To detect and describe suspected cases in the region, the researchers compiled state health surveillance reports, medical records and dengue diagnostic test results for analysis. Available specimens submitted to commercial labs for IgM ELISA testing were forwarded to the CDC for real-time reverse transcription PCR (rRT-PCR) confirmation, and subsequently analyzed for genotypic and phylogenetic characterization. The researchers also conducted household investigations of case-patients, consisting of interviews, questionnaires and blood tests.
Thomas and colleagues identified 264 suspected dengue cases living in southern Texas during the outbreak, almost half of which were detected in October and November. Of these, 20% (n = 53) were laboratory-confirmed. Approximately 17% of IgM-negative specimens submitted for rRT-PCR confirmation were found to be positive. Dengue virus type-1 was detected in 86% of rRT-PCR confirmed samples, while dengue virus type-3 was confirmed in 14%.
Molecular phylogenetic analysis of isolated samples indicated that the virus affecting Mexico and Texas during the epidemic were related to others circulating in Mexico and Central America, they wrote. Of the 49 confirmed cases with available travel history, 53% did not report travel outside of the state within 2 weeks of onset, while the others reported recent trips to Mexico. Approximately 55% of confirmed cases were hospitalized, a rate which the researchers noted was greater than those reported within endemic countries.
Household investigations identified an additional seven persons with evidence of recent dengue infection, as detected by MAC ELISA testing. Five of these also reported no recent travel outside of Texas.
According to Thomas and colleagues, these findings represent the greatest number of locally acquired dengue cases since 1980. However, they wrote, the substantial number of travel-related cases and close relation to the circulating Mexican strain indicate a need for preparation when nearby regions report an epidemic.
“Future dengue epidemics in northern Mexico are likely to result in local [dengue virus] transmission in southern Texas,” the researchers wrote. “Residents of southern Texas should therefore empty, cover or dispose of mosquito breeding sites and use mosquito repellent to avoid mosquito bites. Clinicians should order both molecular and serologic diagnostic testing for suspected dengue patients, and positive results should be reported to public health authorities.”
Officials advise vigilance as Hawaiian outbreak recedes
The most recent outbreak of dengue in the U.S. occurred in Hawaii last year, and resulted in 264 cases of illness, according to the Hawaiian Department of Health’s Disease Outbreak Control Division.
As of April 26, 218 adults and 46 children living on the Big Island were confirmed by the health department to have been infected since Sept. 11, 2015, while 1,643 potential cases were excluded based on test results or unmet case criteria. This outbreak — which led Hawaii County Mayor William P. Kenoi to declare a state of emergency in February — was the first indigenous cluster in the state since 2011.
While no new cases have been identified since the most recent update, health officials are still advising active surveillance due to the potential presence of infectious mosquitoes on the island. – by Dave Muoio
Reference:
State of Hawaii, Department of Health. Dengue Outbreak 2015-2016. http://health.hawaii.gov/docd/dengue-outbreak-2015/. Accessed May 10, 2016.
Disclosure: The researchers report no relevant financial disclosures.