Screening for Transfusion Transmitted Infections - an important aspect in achieving the elimination goals for India
By now, it’s a known fact that every two seconds someone needs blood
and each year thousands of lives are saved by blood transfusions, globally. Having
said that, Transfusion Transmitted Infections (TTIs) are a global health
concern. India has taken significant steps in line with the WHO guidelines to
limit the prevalence of TTIs over the past few years.
According to the latest data registered
by WHO in 2020, of the 118.5 mn blood donations collected globally, 40% were
collected in high-income countries, home to 16% of the world’s population. While
this may give an indication of the number of patients benefitting through blood
transfusions, another important aspect to consider is how many patients
requiring transfusion get timely access to safe blood.
Blood and blood components are
life-saving but at the same time can often result in significant adverse events
including immunologic reactions and infections, which can prove to be fatal. Transfusion
Transmitted Infections (TTIs) are passed on through transfusion of infected
blood donated by apparently healthy and asymptomatic blood donors. TTIs, as we
all know, are very diverse and include different sub-groups of pathogens.
Through today’s blog, we will limit the discussion to few important ones
including Hepatitis B and C virus, HIV (1+2) and Syphilis.
Global prevalence
With every one unit of blood
transfused, there is a 1% chance of transfusion transmitted infections.*
Global prevalence (in mn) of Hepatitis, HIV and Syphilis in 2020
Percentage of patients globally suffering from HIV and Hepatitis post
transmission
While these numbers speak great
volumes on the prevalence of TTIs, the incidence rate is estimated to be
higher, given the asymptomatic and often latent nature of the disease prior to
clinical presentation. Every blood transfusion therefore carries a potential
risk for transmissible diseases.
Another interesting aspect;
according to WHO, the prevalence of TTIs in blood donations in high-income
countries is considerably lower than in low- and middle-income countries. Lack
of awareness, poor availability of screening tests, and limited or
non-existence of surveillance systems could be the possible reasons for this
trend.
The India story
As a signatory to the UN
declaration on Sustainable Development Goals (SDGs), India is committed to
achieving the ‘End of AIDS’ by 2030. Specific fast-track targets, including 75%
decline in new HIV infections from the 2010 baseline value, attainment of
95-95-95 strategy, among others have been identified to support the global AIDS
response by 2030.
As per the India HIV estimation
2019 report**, the overall estimated adult HIV prevalence trend has been
declining in India since its peak in 2000 and has been stabilizing in recent
years.
Prevalence in India (in percentage) suffering from HIV, Hepatitis, STIs
in 2019
Speaking of HBV, the Indian
subcontinent is classified as an intermediate Hepatitis B Virus (HBV) endemic
zone and has 10-15% of the global pool of HBV.
Screening strategies
Safe
blood transfusion services are a cornerstone of an effective high quality
health care system and require organized
infrastructure, properly trained staff, availability of expensive equipment and
good reagents.
Despite current advanced
screening technologies, prevention of TTIs is one of the greatest challenges of
transfusion medicine. Therefore, the WHO recommends that all blood donations should
be mandatorily screened for HIV, hepatitis B, hepatitis C and syphilis, prior
to use. Blood screening should be performed according to quality system
requirements.
The WHO recommends every country to develop its national
screening strategy based on the incidence and prevalence of infection,
infrastructure, cost of screening and available resources. The strategy should
provide specific guidelines on markers to be screened, assays to be used, assay
performance characteristics, quality systems for screening, whether
confirmatory tests should be performed, etc.
Diagnosis of TTIs - selecting the appropriate assay
The diagnosis of TTIs is made
either by demonstrating the presence of virus or viral products in the host,
alternatively by detecting the host response to the virus. The assays most
commonly in use are designed to detect antibodies, antigens or nucleic acid of
the infectious agent. However, not all assays are suitable in all situations
and each assay has its limitations which need to be understood and taken into
consideration when selecting assays. Needless to say, sensitivity and
specificity, ease-of-use, stability and convenience of usage, are some of the
important characteristics to select an assay.
Techniques such as immunoassays
which are based on ELISA, CLIA and rapid testing along with nucleic acid
amplification technology (NAAT) are the main types of assays in use. Since TTIs
are associated with low viral titre, screening through molecular method is
considered the most reliable method for detection. However these tests are
relatively expensive and hence preferred in high-cost settings.
ELISA and CLIA exhibit better and
more consistent performance compared to rapid tests and are preferred for large
number of samples. On the other hand, a rapid test with validated high
sensitivity and specificity is usually chosen for immediate and emergency
testing or in labs with limited resources.
In spite of sensitive methods to detect markers of
TTIs, the problem of false negative results occurs due to prevalence of
asymptomatic carriers, blood donation during ‘window period’, high genetic
variability in viral strains and technical errors.
Currently most pathology labs in
India perform immunoassay testing based on detection of antigens and antibodies
in case of HIV and only antibodies in case of HCV. Leading diagnostic
manufacturers like Transasia Bio-Medicals have introduced 4th
generation assays that are intended for simultaneous detection of antigens and
antibodies, and offer additional advantages that result in early and more
accurate detection of the infection.
Moreover, any 3rd
generation assay usually offers a window period in the range of 15-180 days.
Simultaneous detection of antigen and antibodies, greatly aids in reducing the
window period. For HBsAg, highly sensitive kits are available which increase
the analytical sensitivity of the assay.
Laboratories also prefer to opt
for assays that are easily and fully adaptable on automated processors,
allowing them to reduce the manual intervention, increase reproducibility and
TAT.
Conclusion
In India, while there is a decreasing trend in the deaths
caused due to TTIs, the need of the hour is to control the spread of new
infections, especially with the advent of emerging infectious agents. This is
especially a concern in resource-limited settings. On the positive side, the
government has worked out various policies focused on increasing awareness and
screening and treatment strategies. Significant advancements have been made in
the testing modalities over the years, and diagnostic manufacturers are
providing kits that significantly reduce the window period and offer better
sensitivity and specificity.
Sources:
* https://www.ijcmr.com/uploads/7/7/4/6/77464738/ijcmr_2872_v3.pdf
[1]
World Health Organization. Global Progress
Report on HIV, Viral Hepatitis and Sexually Transmitted Infections, 2021.
Accountability for the Global Health Sector Strategies 2016–2021: Actions for
Impact; Licence: CC BY-NC-SA 3.0 IGO; World
Health Organization: Geneva,
Switzerland, 2021; (accessed on 12 October 2021).
** http://naco.gov.in/hiv-facts-figures
***https://ijdvl.com/lets-not-let-the-guard-down-early-indications-of-syphilis-resurgence/
Authored by:
Ajinkya Upasani
Asst. Product Manager – Immunology
Transasia Bio-Medicals Ltd.
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