Successful control of an infectious disease requires
accurate identification of all infections, whether symptomatic or not.
Achieving this within a reasonable budget in a timely manner is of great
importance for most infectious diseases.
One typical example is HIV. Since many HIV-positive people
are unaware that they are infected with the virus, the virus can be passed on
long before the patient is diagnosed. Of particular concern is the spread of
the disease through blood donation, making it necessary to screen ALL donated
blood in blood banks. For HIV screening, nucleic acid testing (NAT) is
currently the most effective approach as it reduces the risk of false negatives
during the window period. As NAT is relatively expensive, blood is usually
screened using a pooling strategy, which results in a dramatic increase in
throughput and decrease in cost. But the dilution of virus in pooled samples
decreases the effective sensitivity of the test, lengthening the window period
by 4 days.
Malaria is another example. Having achieved remarkable
success, malaria control programs seem to be heading toward elimination.
However, malaria is spread through a mosquito vector, and asymptomatic or
“reservoir” infections may account for 20%-50% of all transmissions. Malaria
screening of walk-in patients typically employs microscopy or rapid diagnostic
tests (RDT). Reservoir infections cannot be identified using passive testing,
and eradication can never be attained if programs focus on testing walk-in
patients. Therefore, active screening with NAT must be adopted in malaria
eradication efforts. Current NATs, however, require specialized skills and are
usually time-consuming. In Yunnan, China, more than 350,000 samples were
screened to find hundreds of infections in 2014. Finishing this task with
current NATs is impractical.
Such diagnostic dilemmas are faced for most infectious
diseases: NAT gives better results, but is usually low-throughput and requires
higher skills and greater expense. High-throughput molecular diagnostic assays
with simplified workflow and improved cost-effectiveness are desperately
In our recent study, we designed a novel RNA quantification
technology, CLIP-PCR, which significantly increased the throughput for clinical
molecular diagnostics with simplified procedures. The operation involves only
mixing, dispensing and decanting - steps that are readily amenable to automation.
And thanks to the selective capture during the test, irrelevant nucleic acids
can be washed off before the signal production procedure, making possible the
adoption of a pooling strategy without compromising assay performance. These benefits
together make CLIP-PCR an ideal approach for sensitive, convenient and
affordable large-scale molecular tests for infectious diseases.
In our abstract for the 2015 AACC annual meeting and our
recent article in Clinical Chemistry,
we described an application of CLIP-PCR to large-scale screening of malaria in
elimination settings. CLIP-PCR identified 14 infections, including 4 reservoirs,
from 3358 samples with <500 tests (in ten 96-well plates), costing
<US$0.60 for each sample and demonstrating an improved approach for malaria
control. We believe, after identifying the proper target for a disease, such as
HIV-I GAG or the 3-X-tail element for HCV, CLIP-PCR is amenable for
high-throughput, sensitive and convenient diagnosis of most, if not all,
diseases. This is all achievable in an ELISA-like workflow!