The number of dengue-related hospitalizations in the United States has tripled in the past decade, according to a recent study.  Using data culled from the National Inpatient Sample, researchers from the University of Iowa Carver College of Medicine conducted a retrospective cohort analysis of all hospital discharges in the United States from 2000 to 2007.

Dengue Mosquito
The investigators identified all primary and secondary cases of dengue, based on ICD-9 codes. The International Classification of Diseases (ICD), Clinical Modification is used to code and classify morbidity data from the inpatient and outpatient records, physician offices, and most National Center for Health Statistics (NCHS) surveys.

“The worldwide number of cases of dengue infection has increased nearly 35-fold in the past half-century,” the researchers said. “Risk for dengue infection to US residents has primarily been posed by travel, [but] because dengue has not been a reportable disease [in this country] until recently, incidence and disease trends are difficult to determine.” Physicians in the United States have been required to report cases of dengue to public health authorities since 2010, according to the CDC website.

The increase in cases was felt by the researchers to not be surprising considering that 1) the number of cases in disease-endemic regions has increased in recent years, and 2) a substantial number of travelers annually enter the US from the tropics and subtropics,” the researchers said."

The researchers found that during the years examined, the estimated number of reported dengue cases went from 81 to 299, a threefold increase (incidence ratio=3.5641; 95% CI, 2.0293-6.6232). Between 2000 and 2007, about 1,250 patients with a median age of 38 years (range, newborn-87 years) were hospitalized for dengue fever. The average length of stay for this cohort was 3 days, (range, 0-35 days). From 2004 to 2007, the Northeast had the highest incidence rate nationwide (P=.0001); all regions experienced otherwise homogeneous incidence rates.

A noted limitation to the study was that it used administrative data devoid of laboratory data and patient travel history. Any cases of outpatient dengue treatment were also missing. “Nevertheless, our results indicate that the decision to make dengue fever a reportable disease in the United States was warranted and that increased vigilance focused on these new surveillance data is needed,” the researchers said.