Dengue seropositivity among blood donors in a tertiary hospital in Kerala, Southern India.

Aim: The aim of this study was to screen blood donors in a tertiary hospital in Kerala for dengue during the period of peak dengue transmission. Materials and
Methods: One hundred and seventy-eight continuous serum samples obtained from asymptomatic blood donors during the monsoon season were subjected to ELISA for Dengue NS1 antigen and dengue immunoglobulin M (IgM) antibodies.
Results: Dengue IgM antibodies were positive in 20 (11.23%) donors and NS1 antigen was positive in 1 (0.56%) donor. The presence of these markers in asymptomatic blood donors showed that they may have had active or subclinical dengue infection at the time of donation or in the recent past. The presence of NS1 in particular raises the possibility that the donor may have been viremic at the time of donation.
Conclusion: The findings of this study suggest the risk of transfusion transmission of dengue during the monsoon in Kerala and strengthen the case for dengue screening among blood donors during this period of high incidence.

INTRODUCTION

Dengue is an arboviral disease whose incidence has surged in recent years in concert with increasing globalization and climate change. A recent study presented a preliminary estimate that 3.9 billion people, in 128 countries the world over, are at risk of dengue.[1] Another estimate suggested that India accounted for 34% of the burden of global dengue in 2010.[2] Dengue is endemic in most of India. The prevalence of four dengue serotypes DEN-1, DEN-2, DEN-3, and DEN-4 has been recorded in Kerala. The mosquito vector Aedes albopictus is widespread in the state.[3] The incidence of dengue in Kerala typically peaks during seasonal outbreaks between May and July during the monsoon season when rainfall is copious.[3]

Several instances of transmission of dengue from asymptomatic donors through transplants and blood transfusions have been recorded.[4-6] Transfusion-transmitted dengue (TTD) is nevertheless a rare entity.[7] Karim et al.[8] in 2017 reported a case where two surgical patients acquired possible TTD from different components obtained from an infected donor. A study conducted in two cities in Brazil during a massive DEN-4 epidemic in 2012 concluded that, during peak periods of transmission in dengue epidemics, as many as, 1%–2% of donations may be positive for dengue viral RNA and 0.3%–0.6% of all transfusions may transmit the virus.[9]

There is no data from southern India regarding dengue seropositivity among blood donors. The present study was undertaken to detect dengue seropositivity among blood donors in a 1350-bedded hospital in Kerala as a preliminary step toward assessing the need for donor screening in a dengue hyperendemic region during the peak transmission period.

MATERIALS AND METHODS

Information on peak incidence of dengue was derived from dengue statistics in our hospital. The number of cases was found to peak in the month of June, during the monsoon. Hence, the study was done prospectively with 178 continuous serum samples obtained from all asymptomatic blood donors who donated blood at our tertiary hospital in the last 2 weeks of June and consented to participate in the study. The sample size was limited by the cost of the testing kits. Institute ethics committee clearance was obtained prior to the commencement of the study. Eligible donors were questioned carefully to rule out recent history of fever. Those samples that tested positive for HIV, hepatitis B virus, hepatitis C virus, malarial antigen, or syphilitic antibodies during routine blood bank screening were excluded.

Four microliter of peripheral blood were collected in tubes without anticoagulant. The tubes were centrifuged at 3000 rpm for 15 min to obtain serum. Sera were then stored in a deep freezer at − 20°C.

NS1 antigen of dengue virus was assayed using two commercial NS1 antigen capture enzyme-linked immunosorbent assays (ELISAs) (Panbio Dengue Early ELISA, and QUALISA Dengue NS1 ELISA).

Anti-dengue immunoglobulin M (IgM) antibodies were detected using commercial IgM capture ELISA (NovaLisa, NOVATEC Immunodiagnostica,).

The samples were tested in accordance with the manufacturer's instructions. Equivocal results were considered negative.

RESULTS

Blood samples were collected from 178 donors aged between 18 and 60 years. Of these, 89 (50%) were aged between 21 and 30 years and 168 (94.4%) were male. Twenty (11.2%) sera were positive for dengue IgM and one (0.6%) tested positive for NS1 antigen [Table 1]. There was no sample that tested positive for both NS1 antigen and IgM antibody.

Table 1

Dengue immunoglobulin M and nonstructural protein 1 positivity among blood donors

Assay	Positive (out of 178) (%)
Dengue IgM ELISA	20 (11.23)
Dengue NS1 ELISA	1 (0.56)

ELISA=Enzyme-linked immunosorbent assays, NS1=Nonstructural protein 1, IgM=Immunoglobulin M

Twelve (57.1%) of the 21 asymptomatic donors who tested seropositive for dengue were aged between 18 and 30 years [Table 2]. Twelve (57.1%) of the 21 donors who tested positive were residents of Ernakulam district in Kerala, India.

Table 2

Age distribution of blood donors

Age group	Number of donors	Dengue IgM-positive	Dengue NS1-positive
18-30	108	11	1
31-40	49	8	0
41-50	20	1	0
51-60	1	0	0

NS1=Nonstructural protein 1, IgM=Immunoglobulin M

There were no signs of transfusion-transmitted illness in the patients who were transfused with the IgM-positive units. The recipients were not tested for dengue. The fate of the blood unit from the donor who tested NS1-positive was traced on the completion of the study to look for evidence of transfusion transmission. It was found that the unit had been discarded, not transfused, even though the fact of NS1 positivity had not been known at the time of discarding.

DISCUSSION

Dengue has an incubation period of 4–10 days.[10] Viremia can precede the onset of fever by 2–3 days and can last up to 8 days after illness onset.[11] The Centers for Disease Control advises that as many as 50% of all dengue infections are asymptomatic.[12] The proportion of dengue infections that are asymptomatic differs both geographically and from one dengue serotype to the other. The level of viremia in asymptomatic as compared to symptomatic dengue infections has not been studied widely, though viremia has been assumed to be lower in asymptomatic infections in some studies.[13]

A PubMed search using the terms “dengue,” “blood donors,” and “India” revealed 2 studies from northern India and 1 from western India on dengue seropositivity in blood donors. There was no data from the southern part of the country. The present study aimed at estimating the rates of dengue seropositivity among asymptomatic blood donors in a tertiary hospital in Kerala, a southern Indian state, as a pilot study, with a view to assessing the risk of transfusion transmission during the monsoon season. Twenty-one (11.7%) out of 178 asymptomatic donors were seropositive. Of these, 20 donors (11.2%) tested dengue IgM positive, suggesting either active infection or infection that occurred within the preceding 3 months. The rate of dengue IgM positivity in this study (11.2%) is similar to that (13.5%) detected in a study in northern India that involved 200 blood donors.[14]

There was one donor (0.56% of all donors) who tested NS1-positive in the present study. The presence of antigenemia in this donor is significant as it implies recent infection and the potential to transmit the virus. Mangwana[15] looked for NSI antigenemia among 1708 blood donors in a study conducted in a tertiary care center in north India and found none positive.

NS1 antigen can be detected from the day of illness onset and can persist up to 18 days.[16] The period of antigenemia overlaps the period of viremia. However, the sensitivity of NS1 declines in secondary dengue infections.[17] NS1 antigen has been postulated to play a role in the replication of dengue virus.[18] Several studies report that dengue viral loads and disease severity are higher among NS1-positive patients.[192021]

The seroprevalence of dengue among blood donors has been reported from several studies worldwide. El-Shemi et al. reported a seropositivity of 5.3% for dengue NS1 antigen, 5.5% for dengue IgM antibody, and 38.9% for dengue IgG antibody among blood donors in Makkah, Saudi Arabia.[22]

Aubry et al. studied the presence of IgG against each of the four dengue serotypes in 593 donors in French Polynesia using an indirect ELISA which employed recombinant envelope glycoprotein antigens. They found that DEN-1 seroprevalence was the highest and that 80.3% of the donors had antibodies against one or the other serotype.[23]

A limitation of the present study includes the lack of molecular confirmation of viremia among donors. The confirmation of viremia among blood donors by nucleic acid detection and its quantification by viral load assay would strengthen the case for screening for dengue among blood donors in outbreak situations.

Transfusion transmission is a looming threat during dengue epidemics. There are several proven cases of TTD recorded in literature.[79] Yet dengue is not considered enough of a risk to transfusion safety to warrant routine screening.

Sabino et al., in a study of blood transfusions during a dengue epidemic in Brazil, reported that only a third of the dengue-positive transfusions transmitted the virus.[9] Most recipients of TTD who went on to manifest clinical symptoms have had benign courses of the illness. However, instances of severe dengue with hemorrhagic manifestations have been reported.[4724] The American Association of Blood Banks Committee recently included dengue, among other emerging infectious agents such as vCJD, hepatitis E virus, Chikungunya virus, and Babesia as high priority for increased monitoring in American blood supply.[25]

The benefits of pathogen Inactivation systems were convincingly demonstrated by the use of the intercept technology for platelets during the Chikungunya outbreak in Reunion Island in 2006 and the recent Zika virus outbreak in north and south America.[26] As the number of recognized transfusion-transmissible pathogens increases, the adoption of pathogen inactivation methods may eventually prove more economical than expanding the number of tests for donor screening.[27] But, for the moment, many blood banks in developing countries cannot afford the implementation of these technologies.

Deferral measures for donors with history of fever are practised in countries such as Australia, New Zealand, Singapore, and Hong Kong and Sri Lanka. These measures do not preclude transfusion transmission from viremic donors who may be asymptomatic. They have found to be less feasible in dengue-endemic countries when compared to nonendemic countries as their lack of specificity in endemic countries would lead to an unwarranted loss of donors.[6]

CONCLUSION

Considering these facts and the unavailability of antiviral drugs against dengue, proactive measures must be taken to ensure blood safety. Routine screening for dengue among blood donors is not the norm as it is not cost-effective. However, in the light of the substantial numbers of seropositive blood donors detected during the peak dengue season in Kerala, screening for dengue during these spells may be prudent in this hyperendemic area to prevent transfusion-transmitted infections.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.