Dengue risk factor distribution in Harris County, Texas

As an important emerging arboviral disease in Texas and throughout the world, dengue fever has the potential to make a re-emergence in the Harris County/Houston metropolitan area. Harris County has seen dengue epidemics in the past. The area has a competent vector, Aedes aegypti, capable of transmission of the virus should it be introduced. It is important to examine areas of highest risk for dengue emergence and transmission in Harris County so that surveillance and educational programs can be properly implemented. This study uses mapping software to visually represent risk factor information with areas of known Ae. aegypti populations. This study focused on known demographic risk factors such as race/ethnicity, place of birth, gender as well as socioeconomic status represented by educational attainment and income. This study found that there are several areas, particularly in central Harris County that are at particular risk for dengue transmission. The findings support the hypothesis that in areas of lower socioeconomic status there were increased populations of foreign born populations, Hispanic populations, and identified locations of a competent vector present. These findings suggest that more specific surveillance of Ae. aegypti, testing of the mosquitoes for dengue virus, and active surveillance for human cases should be implemented in these areas. ^

Evidence of secondary dengue infection and potential for association with clinical depression in a subset of a randomly selected cohort in South Texas

Globally, dengue is an emerging disease resulting in an estimated 50 million new cases and 22, 000 deaths each year. Anecdotally, depression has been reported as a possible sequelae of dengue virus infection. To test the association, we performed a cross-sectional analysis in a selected sub-set of participants from the Cameron County Hispanic Cohort (CCHC) in South Texas. All study subjects in the analysis had Center for Epidemiological Studies Depression scale (CES-D) scores and were tested for dengue antibodies using stored plasma. We found that 5.0% of participants tested either positive or equivocal for anti-dengue IgG antibodies using the capture antibody test, which detects acute secondary infections. Logistic regression identified that evidence of acute secondary dengue infection was not associated with depression (Odds Ratio [OR] = 0.97, 95%Confidence Interval [CI] 0.47-1.98); however, both being female (OR = 1.53, 95%CI 1.09-2.15) and obese body mass index (BMI > 30) (OR = 1.84, 95%CI 1.19-2.84) were associated with depression. ^

Aedes aegypti, Aedes albopictus, and Dengue virus in Harris county: An estimate of risk

Recent outbreaks of dengue fever (DF) along the United States/Mexico border, coupled with the high number of reported cases in Mexico suggest that there is the possibility for DF emergence in Houston, Texas1,2. To determine the presence of DF, populations of Aedes aegypti and Aedes albopictus were identified and tested for dengue virus. Maps were created to identify "hot spots" (Figure 1) based on historical data on Ae. aegypti and Ae. albopictus, demographic information, and locations of human cases of dengue fever. BG Sentinel Traps®, in conjunction with BG Lure® attractant, octanol and dry ice, were used to collect mosquitoes, which were then tested for presence of dengue virus using ELISA techniques. All samples tested were negative for dengue virus (DV). Survival of DV ultimately comes down to whether or not it will be vectored by a mosquito to a susceptible human host. The presence of infected humans and contact with the mosquito vectors are two critical factors necessary in the establishment of DF. Historical records indicate the presence of Ae. aegypti and Ae. albopictus in Harris County, which would support localized dengue transmission if infected individuals are present.^ (1) Brunkard JM, Robles-Lopez JL, Ramirez J, Cifuentes E, Rothenberg SJ, Hunsperger EA, Moore CG, Brussolo RM, Villarreal NA, Haddad BM, 2007. Dengue fever seroprevalence and risk factors, Texas-Mexico border, 2004. Emerg Infect Dis 13: 1477-1483. (2) Ramos MM, Mohammed H, Zielinski-Gutierrez E, Hayden MH, Lopez JL, Fournier M, Trujillo AR, Burton R, Brunkard JM, Anaya-Lopez L, Banicki AA, Morales PK, Smith B, Munoz JL, Waterman SH, 2008. Epidemic dengue and dengue hemorrhagic fever at the Texas-Mexico Border: results of a household-based seroepidemiologic survey, December 2005. Am J Trop Med Hyg 78: 364-369.^

Suspected outbreak of dengue fever in Houston: Clinical characteristics and determination of autochthonous transmission between 2003 and 2005

Houston, Texas maintains the appropriate climate and mosquito populations to support the circulation of dengue viruses. The city is susceptible to the introduction and subsequent local transmission of dengue virus with its proximity to dengue-endemic Mexico and the high degree of international travel routed through its airports. In 2008, a study at the University of Texas School of Public Health identified 58 suspected dengue fever cases that presented at hospitals and clinics in the Houston area. Serum or CSF samples of the 58 samples tested positive or equivocal for the presence of anti-dengue IgM antibodies (Rodriguez, 2008). Here, we present the results of an investigation aimed to describe the clinical characteristics of the 58 suspected dengue fever cases and to determine if local transmission had occurred. Data from medical record abstractions and personal telephone interviews were used to describe clinical characteristics and travel history of the suspected cases. Our analysis classified six probable dengue fever cases based on the case definition from the World Health Organization. Three of the probable cases for which we were able to obtain travel history had not recently traveled to an endemic area prior to onset of symptoms suggesting the illnesses were locally acquired in Houston. Further analysis led us to hypothesize that additional cases of dengue fever are present in our study population. Fifty-one percent of the study population was diagnosed with meningitis and/or encephalitis. Sixty percent of the individuals who received a lumbar puncture had abnormal CSF. Together these findings indicate viral infection with neurological involvement, which has been reported to occur with dengue fever. Among the individuals who received liver enzyme analysis, 54% had evidence of abnormal liver enzyme levels, a clinical sign commonly observed with dengue. Our results indicate that a suspected outbreak of dengue fever with autochthonous transmission occurred in the Houston area between 2003 and 2005. ^

The epidemiology of dengue among children less than 18 months of age in Puerto Rico, 1999--2011

Between 1999 and 2011, 4,178 suspected dengue cases in children less than 18 months of age were reported to the Centers for Disease Control and Prevention Dengue Branch in Puerto Rico. Of the 4,178, 813 were determined to be laboratory-positive and 737 laboratory-negative. Those remaining were either laboratory-indeterminate, not processed or positive for Leptospira . On average, 63 laboratory-positive cases were reported per year. Laboratory-positive cases had a median age of 8.5 months. Among these cases, the median age for those with dengue fever was 8.7 months and 7.9 months for dengue hemorrhagic fever. Clinical signs and symptoms indicative of dengue were greatest among laboratory-positive cases and included fever, rash, thrombocytopenia, bleeding manifestations, and petechiae. The most common symptoms among patients who were laboratory-negative were fever, nasal congestion, cough, diarrhea, and vomiting. Using the 1997 WHO guidelines, nearly 50% of the laboratory-positive cases met the case definition for dengue fever, and 61 of these were further determined to meet the case definition for dengue hemorrhagic fever. In comparison, 15% of laboratory-negative cases met the case definition for dengue fever and less than 1% for dengue hemorrhagic fever. None of the laboratory-positive or laboratory-negative cases met the criteria for dengue shock syndrome.^

Dengue transmission risk maps of the continental United States

Dengue fever is a strictly human and non-human primate disease characterized by a high fever, thrombocytopenia, retro-orbital pain, and severe joint and muscle pain. Over 40% of the world population is at risk. Recent re-emergence of dengue outbreaks in Texas and Florida following the re-introduction of competent Aedes mosquito vectors in the United States have raised growing concerns about the potential for increased occurrences of dengue fever outbreaks throughout the southern United States. Current deficiencies in vector control, active surveillance and awareness among medical practitioners may contribute to a delay in recognizing and controlling a dengue virus outbreak. Previous studies have shown links between low-income census tracts, high population density, and dengue fever within the United States. Areas of low-income and high population density that correlate with the distribution of Aedes mosquitoes result in higher potential for outbreaks. In this retrospective ecologic study, nine maps were generated to model U.S. census tracts’ potential to sustain dengue virus transmission if the virus was introduced into the area. Variables in the model included presence of a competent vector in the county and census tract percent poverty and population density. Thirty states, 1,188 counties, and 34,705 census tracts were included in the analysis. Among counties with Aedes mosquito infestation, the census tracts were ranked high, medium, and low risk potential for sustained transmission of the virus. High risk census tracts were identified as areas having the vector, ≥20% poverty, and ≥500 persons per square mile. Census tracts with either ≥20% poverty or ≥500 persons per square mile and have the vector present are considered moderate risk. Census tracts that have the vector present but have <20% poverty and <500 persons per square mile are considered low risk. Furthermore, counties were characterized as moderate risk if 50% or more of the census tracts in that county were rated high or moderate risk, and high risk if 25% or greater were rated high risk. Extreme risk counties, which were primarily concentrated in Texas and Mississippi, were considered having 50% or greater of the census tracts ranked as high risk. Mapping of geographic areas with potential to sustain dengue virus transmission will support surveillance efforts and assist medical personnel in recognizing potential cases. ^