Date Published: July 01, 2012
Publisher: The American Society of Tropical Medicine and Hygiene
Author(s): Katherine L. Anders, Nguyen Minh Nguyet, Nguyen Than Ha Quyen, Tran Van Ngoc, Ta Van Tram, Tran Thi Gan, Nguyen Thanh Tung, Nguyen Thi Dung, Nguyen Van Vinh Chau, Bridget Wills, Cameron P. Simmons.
Non-invasive specimens for dengue diagnosis may be preferable where venous blood is difficult to collect and/or process, such as community-based or remote settings or when sampling from young children. We evaluated the performance of oral swabs and dried blood spots (DBS), compared with plasma, in diagnosing acute dengue and screening for past dengue virus (DENV) exposure. DENV-specific immunoglobulin (Ig) M, IgG, and NS1 antigen were detected both in oral swabs and DBS from acute patients. Oral swabs were less sensitive (IgM: 68.7%, IgG: 91.9%, NS1: 64.7%), but retained good specificity (100%, 92.3%, 95.8%, respectively) compared with plasma. DBS displayed high sensitivity (IgM: 100%, IgG: 96%, NS1: 100%) and specificity (IgM: 75%, IgG: 93%). DENV RNA was amplified from DBS (sensitivity 95.6%) but not from oral swabs. DENV-IgG (indicative of past flavivirus exposure) were detected with moderate sensitivity (61.1%) but poor specificity (50%) in oral swabs from healthy volunteers. Dried blood spots allow sensitive and specific diagnosis of acute dengue by serological, molecular, and antigen detection methods. Oral swabs may be an adequate alternative where blood cannot be collected.
In most dengue-endemic countries, clinical management and epidemiological surveillance of dengue cases is based on a clinical diagnosis, with only a small proportion of cases receiving laboratory confirmation. Greater availability of timely, sensitive, and specific diagnostics for dengue may improve patient management, including the identification and appropriate treatment of patients with diseases other than dengue, and improve the accuracy of surveillance data. Serological assays can detect dengue virus (DENV)-specific immunoglobulin (Ig) M or IgG from around 4–5 days after fever onset. Diagnosis by reverse transcription-polymerase chain reaction (RT-PCR) or, less commonly, virus isolation is possible early in infection but is expensive and is rarely used in routine management. More recently, enzyme-linked immunosorbent assay (ELISA)-based and lateral flow rapid tests for detection of DENV NS1 antigen have been shown to have good specificity for diagnosis of early acute dengue, although their sensitivity was dependent on the infecting serotype and the host humoral immune response.1 The sensitivity of all dengue diagnostic assays depends on the timing of sample collection. Venous blood collection is typically required for all of the previous dengue diagnostic methods. Although this is relatively straightforward in a clinical setting, it requires expertise and equipment for sample collection, processing, and storage, which may be lacking in community-level or remote settings. Furthermore, alternatives to venous blood collection may be preferable in certain populations such as young children, or in serosurveillance studies in healthy volunteers.
Oral swab samples and DBS were evaluated as alternatives to plasma for the diagnosis of acute dengue and for screening for past exposure to dengue virus. DENV-specific antibody and NS1 antigen were detected both in oral swab samples and DBS, using standard diagnostic assays. DENV RNA was amplified from DBS but not from oral swabs. There was little loss of sensitivity or specificity in using DBS compared with plasma. Oral swabs suffered from a loss of sensitivity, but retained good specificity.