Short CommunicationAbstract
With the result of the various studies on the COVID issue, our view shows that determination of Cycle Threshold (Ct) value will help in managing COVID positive cases efficiently and economically during this time of high spread of pandemic. At large, COVID has created chaos and health sector facing extreme shortages of resources and not enough infrastructures to keep COVID patients in country like Nepal and other LMICs. Hence segregating COVID positive cases according to the viral load i.e.; Ct value will help us managing the cases without much stress on the nearly flooded hospitals and we can even easily monitor the cases along with their contacts.
Keywords:COVID; Cycle Threshold Value; LMICs; RT-PCR
Short Communication
Cycle Threshold in RT-PCR: A Relevance to Low-Middle -Income Countries
The rapid spread of infection has devastated the already weak
health care system of Low-Middle -Income Countries (LMICs) and
has brought chaos in all around the world. The hospitals, health
centers are full of the infected patients, the health workers who
were already lesser in numbers have grown lesser due to falling
prey to this virus. The chaotic situation is echoed in World Health
Organization (WHO) as well. It has updated its policy so many
times and so rapidly that it has got trapped in its own confusion.
Firstly, the confusion on the ‘human-to human’ transmission back
during month of December last year, then lack of the guidance on
safety measures among public and health workers, later denying
of COVID as ‘airborne’ transmission and later again accepting it
has all affected on the formulation of health policies in LMICs that
depend heavily on WHO guidelines. Hence, it is imperative to have
the large-scale research on drugs, diagnosis, and public health
safety measures by independently or together by all nations to have
clarity in management. This clarity will help a lot to the countries in
early and accurate diagnosis of COVID.
The detection of COVID infection is based on identifying the
genetic material of COVID virus or finding the immune response
to the COVID infection. The detection of antibody production
is the simplest way to diagnose but it is an indirect way and the
different techniques utilized until now shows large variability in
antibody detection and thus specificity and sensitivity are low and
inconsistent and so not very useful for COVID detection. The direct
way, that is, identifying the genetic material of the virus seems the
best and most reliable way to detect the presence of the virus. The
method used for identifying genetic material from COVID virus is a
real-time polymerase chain reaction (RT-PCR).
RT-PCR is the most accepted standard test for detection of
COVID infection [1,2]. The test enables early detection of viral genes
from clinical samples collected called swab. However, regardless of
the method used, the sensitivity and specificity of the various RTPCR
are not 100%. The sensitivity is estimated to be approximately
70% and specificity, around 95% [3]. The accuracy of viral swabs
varies depending on the site and quality of sampling. In a study
of 205 patients, it was seen that highest sensitivity was seen in
broncheo-alveolar lavage (93%) while lowest sensitivity was seen in throat swabs (32%) and nasopharyngeal swab was in-between
(67%) [4]. Similarly, other factor that may interfere with the result
is the viral load of the sample (type of material collected, and the
disease severity [5].
If the RT-PCR test result is positive, then it allows the clinicians
and public health professionals to isolate the patient as soon
as possible and prevent spread of the viral infection. The Cycle
threshold (Ct) value of a RT-PCR is the number of cycles at which
fluorescence of the PCR product is detectable over the background
signal [6]. The Ct values are inversely proportional to the amount
of genetic material (RNA) in the sample which means lower Ct
values may be associated with more viral load and worse course of
illness and outcomes and vice versa. The infectivity correlated with
Ct value (Ct above 33 to 34 are not contagious) [7]. Although few
disparities in Ct value and positivity in RT-PCR exist [8], the Ct value
can be useful in predicting the clinical course and prognosis of
patients. This will help health workers to categorize and prioritize
the COVID patients to provide appropriate treatment and minimize
risk.
The LMICs including Nepal has poor health system. The health
costs are borne by the people themselves. The number of ICU and
the available bed to the population ratio is frightening low. There is
lack of proper quarantine or isolation facility. There are extremely
low COVID dedicated hospitals. Nepal is leading its population
towards the unpleasant situation of poorly controlled infection.
The only protocol that Nepal had followed strictly was lockdown
as it was seen effective in many other countries. Yet, the cities with
high population density have been badly infected with this virus.
However, approach of contact tracing, testing and treatment has
been disappointing. The Ct value in RT-PCR testing thus can be
very useful in management of cases as it can help us segregate
based on severity and viral load [8]. The group with high Ct can be
persuaded for home or other proper quarantine while those with
low Ct value can be isolated in the stricter way and thus severe
cases can be properly managed in the hospital. We understand the
variable Ct value in different RT-PCR method, and hence suggest the
researchers to focus on working out to bring one uniform Ct value
that can help us determine the infectivity of the patient. This will
prove very economical of LMICs including Nepal.
Presentation at a Meeting
None
Conflicting Interest
None to declare.
References
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