One negative control, one reactive control and calibrators in triplicate format were used in each run according to the manufacturer’s instructions. Antibody testing was done with Panbio Dengue IgM capture ELISA (Inverness Medical Innovations, Australia) and Dengue IgG capture ELISA (Inverness Medical Innovations Australia) kits.

In the present study, we focussed exclusively on patients with reactive anti-dengue virus IgG test in the absence of IgM antibodies or NS1 antigen.īoth IgG and IgM ELISA tests were performed on a fully automated EVOLIS microplate system (Bio-Rad, USA). This is because a single reactive anti-dengue IgG capture ELISA test (GAC-ELISA) in the absence of IgM antibodies or NS1 Ag may denote current infection or past exposure to the virus ( 2, 3, 8). The above two facts combine to result in a non-reactive IgM and NS1Ag test with a reactive IgG result leaves the diagnosis uncertain. In those patients who are IgG sero-reactive the otherwise reliable NS1 antigen test has a poorer sensitivity than usual ( 1, 4, 7). In a group of secondary dengue patients, the IgM response will transiently develop or occurs later than IgG antibodies ( 2, 11). Development of anti-dengue IgG antibodies along with increased IgM is known to occur in secondary dengue infections ( 1, 3). WHO recommends that a confirmatory acute dengue diagnosis by serological means needs IgM seroconversion or a four-fold increase of IgG antibody titers in paired sera ( 3). However, in many laboratories only one serum sample is received for Dengue antibody testing ( 6, 13). ELISA formats are usually preferred where a rise of IgG titer can be estimated from a significant rise in the optical density (OD) values in paired samples. Neutralization assays for detection of IgG antibodies are prohibitive in terms of cost and manpower for routine laboratories ( 2). Anti-Dengue IgG antibodies persist for a long time even up to years ( 3, 12). In secondary dengue infections, IgG titers rise to extremely high levels (much higher than in primary infections) from the day 7 of fever to the next two weeks ( 9, 11). Anti-dengue virus IgG starts rising during 5–7 days after primary infection and even earlier in secondary infections ( 9, 11, 12) and the highest IgG titers appear during the 3 rd week of a primary infection. The use of serum anti-Dengue IgG antibodies lies in demonstration of a four-fold rise in antibody titer in paired serum samples ( 2, 3, 8). However this response is not uniform and IgM may disappear early in some cases ( 10). Most authorities agree that IgM anti-Dengue antibodies usually persist for 2–6 months ( 6– 11) with a median time period of 179 days for primary and 139 days for secondary infections ( 10). False diagnosis of dengue may be due to the persisting IgM antibodies originated from a previous infection ( 2, 8). Furthermore, a single reactive IgM or IgG anti-Dengue virus test is only suggestive for dengue infection ( 2, 7, 8). NS1 Ag may be undetectable especially in secondary dengue cases when anti-NS1 antibodies form immune complexes and hinder their detection ( 4, 7). A reactive NS1 Ag test occurs in dengue patients during days 1–9 of fever occurrence but it has a poor sensitivity ( 4– 7) and is also sometimes non-specific ( 6, 7). NS1 antigen (NS1 Ag) test and IgM capture ELISA (MAC-ELISA) are the most common modalities of diagnosis in clinical practice ( 2).

Specific diagnosis of dengue fever is based on antigen testing, serology, costly molecular methods (RT-PCR) and prohibitively expensive and laborious virus isolation ( 2, 3).

Dengue fever, a fearsome arboviral infection, has the highest burden in South Asia and is especially menacing in large Indian metropolises ( 1).

Igg reactivity