Unsuspected Dengue and Acute Febrile Illness in Rural and Semi-Urban Southern Sri Lanka

Megan E. Reller

, Champika Bodinayake, Ajith Nagahawatte, Vasantha Devasiri, Wasantha Kodikara-Arachichi, John J. Strouse, Anne Broadwater, Truls Østbye, Aravinda de Silva¹, and Christopher W. Woods¹

Author affiliations: Johns Hopkins University School of Medicine, Baltimore, Maryland, USA (M.E. Reller, J.J. Strouse); Medical Faculty of University of Ruhuna, Galle, Sri Lanka (C. Bodinayake, A. Nagahawatte, V. Devasiri, W. Kodikara-Arachichi); University of North Carolina School of Medicine, Chapel Hill, North Carolina, USA (A. Broadwater, A. de Silva); Duke University School of Medicine, Durham, North Carolina, USA (T. Østbye, C.W. Woods)

Abstract

Dengue virus (DENV), a globally emerging cause of undifferentiated fever, has been documented in the heavily urbanized western coast of Sri Lanka since the 1960s. New areas of Sri Lanka are now being affected, and the reported number and severity of cases have increased. To study emerging DENV in southern Sri Lanka, we obtained epidemiologic and clinical data and acute- and convalescent-phase serum samples from patients >2 years old with febrile illness. We tested paired serum samples for DENV IgG and IgM and serotyped virus by using isolation and reverse transcription PCR. We identified acute DENV infection (serotypes 2, 3, and 4) in 54 (6.3%) of 859 patients. Only 14% of patients had clinically suspected dengue; however, 54% had serologically confirmed acute or past DENV infection. DENV is a major and largely unrecognized cause of fever in southern Sri Lanka, especially in young adults.

Dengue virus (DENV), with 4 antigenically distinct serotypes (DEN1–4), is the most common cause of arboviral disease; ≈50 million cases of dengue occur annually in >100 countries (1). Manifestations of dengue infection range from asymptomatic or mild febrile illness to circulatory failure and death from dengue hemorrhagic fever (DHF). Urbanization and geographic expansion of the primary vector for DENV, Aedes aegypti, have fueled the current global dengue pandemic (2).

DENV has been documented in the Indian subcontinent since the 1960s, and there are recent reports of DENV in new areas and of severe disease (2,3). Epidemic dengue was first recognized in Colombo, the capital of Sri Lanka, in 1965–1966 (4). Outpatient, clinic-based surveillance at Colombo’s Lady Ridgeway Children’s Hospital during 1980–1984 found dengue accounted for 16% of acute febrile illness, among which 66% were secondary (recurrent) dengue cases. A 1980–1985 school-based study found a baseline DENV seroprevalence of 50% in Colombo and a 6-month dengue incidence of 15.6%, of which 37% were secondary cases (4). In the early 1980s, severe dengue was rare in Sri Lanka: <10 reported cases were DHF (4). However, since 1989, many cases of DHF have been reported from the heavily urbanized western coastal belt of Sri Lanka, which includes Colombo (5), and cases have recently been reported elsewhere in the country.

DENV began emerging in southern Sri Lanka recently. To define the epidemiology of dengue in this previously unstudied region, we prospectively enrolled patients seeking care for acute febrile illness at a local hospital. Study participants lived in Galle, a seaport city (population 100,000), and the surrounding coastal plain and heavily vegetated foothills at the southernmost tip of the island nation. During the study months, the temperature ranged from highs of 27.5°C to 32°C and lows of 24°C to 26°C, and rainfall was variable (mean 301 mm, range 36–657 mm).