It is hugely challenging to provide a quality service in the face of overwhelming demand, with a workforce affected by COVID-related restrictions and absences, and when personal protective equipment or laboratory consumables may only be unpredictably available. It is in everyone's interests to divert resources spent on unnecessary testing toward testing that has a genuine clinical and public health impact
Like in many other countries, COVID-19 has Nepal in a chokehold. The number of cases outstrips the capacity of public health, diagnostic and inpatient resources. When resources are limited, stewardship of those resources becomes critical. Indications for testing for SARS CoV2, the virus that causes COVID-19, are detailed in Nepal's National Testing Guidelines.
The gold standard test for SARS CoV2 is reverse transcriptase polymerase chain reaction (RT-PCR) and is usually performed on a throat swab or combined nasal and throat swab. Though highly accurate, it is not a perfect test.
It requires relatively expensive equipment and scientific expertise to perform, limiting it largely to centralised laboratories.
The turnaround time of the result can be slow - samples need to be transported to the lab, it often takes several hours to perform the test, and the result generated then needs to be reported to the person requesting the test. The accuracy of the result is dependent on how well the swab was taken. Even a well taken swab may occasionally give a falsely negative result and, more rarely still, a false positive result.
Perhaps the most difficult area in COVID-19 testing lies in the interpretation of positive results. The test doesn't detect the SARS CoV2 virus per se, it detects its genetic building blocks, known as RNA. So while an RT-PCR test can detect an active, infectious virus, it can also detect fragments of viral RNA that are no longer capable of causing infection. The implication of this is that a positive RT- PCR test cannot, on its own, tell you whether a patient is infective or non-infective.
To tell if the infectious virus is present, it needs to be cultured - grown within cells in a research laboratory.
Where a patient is displaying symptoms of COV- ID-19, interpretation is usually easy. A positive test means that the patient is highly likely to have COV- ID-19. But when a patient has no symptoms, interpretation is more difficult.
A positive result could reflect the pre-symptomatic phase – roughly 48 hours before developing symptoms when patients are highly infectious.
It could reflect detection of traces of non-infective viral material in someone who has recently had COV- ID-19 without realising it. It could reflect one of the minority of people who have COVID-19 but never develop symptoms (asymptomatic carriers). It also could represent a false positive result. Interpreting a positive result, therefore, depends on a number of factors including the patient's symptoms, whether they have been exposed to COVID, and their previous testing history.
A key aspect in managing COVID-19 is to determine when a patient is no longer infectious and infection control precautions can be relaxed. The World Health Organisation (WHO) originally recommended a testbased solution to this problem.
Where a patient had clinically recovered, two sequential negative RT-PCR tests at least 24 hours apart were required. However, in June 2020, the WHO advocated an approach that did not require testing. For patients with no symptoms, this was simply 10 days from their positive test. For those with symptoms, it was 10 days after the onset of symptoms, with at least three additional days once symptoms had resolved.
There were good reasons for making this change.
First, research laboratories have shown that an infectious virus has only exceptionally rarely been isolated from patients longer than nine days after infection.
The peak time of infectivity is just before symptoms start and drops quickly within a few days of illness.
Second, it was recognised that many patients persistently or intermittently tested positive by RT-PCR despite their symptoms having improved. This caused uncertainty, anxiety, unnecessarily prolonged isolation and delays in accessing other health care needs in a patient group unlikely to present a risk of infection to others. Third, requiring routine follow-up RT-PCR testing places an avoidable burden on a limited and precious testing resource.
The WHO non-test based approach has been adopted by Nepal as well as having global support (including the United States Centre for Disease Prevention and Control, Health Protection Scotland, Public Health England and the European Centre for Disease Prevention and Control).
I would urge adherence with the national guidance in following a non-test approach to relaxing infection control precautions for patients with COVID in Nepal.
It is a sensible and safe way of freeing up the much-needed RT-PCR capacity, while reducing the anxiety and unnecessary isolation associated with trying to interpret persistently positive results. In addition to the well-publicised pressures on clinical frontline staff and resources, similar profound pressures are placed on non-clinical staff, procurement processes and national supply chains.
Laboratory staff in particular will be under immense strain. It is hugely challenging to provide a quality service in the face of overwhelming demand, with a workforce affected by COVID-related restrictions and absences, and when personal protective equipment or laboratory consumables may only be unpredictably available. It is in everyone's interests to divert resources spent on unnecessary testing toward testing that has a genuine clinical and public health impact.
While a rational, co-ordinated national testing programme is vital to curtail the spread of SARS CoV2, it cannot be successful in isolation.
Testing must be part of a broader COVID-19 strategy that includes adherence to public health measures, such as social distancing, mask wearing and self-isolation of symptomatic persons.
Dr Robertson, MD FRCPath, is Microbiology Consultant at University Hospital Crosshouse, Kilmarnock, Scotland
A version of this article appears in the print on June 14, 2021, of The Himalayan Times.
