AJIC:Intermittent Positive Testing For MERS-CoV
#13,615
One of the nagging questions regarding the incidence and spread of MERS-CoV on the Arabian Peninsula is just how well surveillance and testing programs are picking up cases.
In the past we've seen some analyses suggesting that only a fraction of MERS cases are likely diagnosed, including:
Last week, in JIDC: Atypical Presentation Of MERS-CoV In A Lebanese Patient,we looked at evidence that the virus can present with non-respiratory symptoms, and two months ago - in Evaluation of a Visual Triage for the Screening of MERS-CoV Patients - we looked at a highly critical review of the screening methods used by the Saudis for selecting patients for MERS testing.
Today we've another study - in press for the American Journal of Infection Control - that finds intermittent (positive-negative-positive) lab results for MERS in a substantial number of cases.
A subtle reminder that while `no' should always mean no - sadly - for lab tests, it isn't always so.
http://afludiary.blogspot.com/2018/1...sting-for.html
#13,615
One of the nagging questions regarding the incidence and spread of MERS-CoV on the Arabian Peninsula is just how well surveillance and testing programs are picking up cases.
In the past we've seen some analyses suggesting that only a fraction of MERS cases are likely diagnosed, including:
- In November of 2013, we looked at a study published in The Lancet Infectious Diseases, that estimated for every case identified, there are likely 5 to 10 that go undetected.
- In 2015, when Saudi Arabia had recorded fewer than 1200 MERS cases, a seroprevalence study (see Presence of Middle East respiratory syndrome coronavirus antibodies in Saudi Arabia: a nationwide, cross-sectional, serological study by Drosten & Memish et al.,) suggested nearly 45,000 might have been infected.
- And a 2016 study (see EID Journal: Estimation of Severe MERS Cases in the Middle East, 20122016)suggested that as much as 60% of severe Saudi MERS cases go undiagnosed.
Last week, in JIDC: Atypical Presentation Of MERS-CoV In A Lebanese Patient,we looked at evidence that the virus can present with non-respiratory symptoms, and two months ago - in Evaluation of a Visual Triage for the Screening of MERS-CoV Patients - we looked at a highly critical review of the screening methods used by the Saudis for selecting patients for MERS testing.
Today we've another study - in press for the American Journal of Infection Control - that finds intermittent (positive-negative-positive) lab results for MERS in a substantial number of cases.
Sarah H. Alfaraj, MD, Jaffar A. Al-Tawfiq, MD, Ziad A. Memish, MD, FRCPC, FACP, FRCPE, FRCPL
Background
Middle East respiratory syndrome coronavirus (MERS-CoV) continues to be reported from the Kingdom of Saudi Arabia. Data on the phenomenon of intermittent positive results for MERS-CoV on reverse-transcription polymerase chain reaction (RT-PCR) with negative results in between are lacking.
Middle East respiratory syndrome coronavirus (MERS-CoV) continues to be reported from the Kingdom of Saudi Arabia. Data on the phenomenon of intermittent positive results for MERS-CoV on reverse-transcription polymerase chain reaction (RT-PCR) with negative results in between are lacking.
Here we describe cases with intermittent positive MERS-CoV test results and highlight the required number of tests to rule out or rule in MERS-CoV infection based on a large retrospective cohort of patients with confirmed MERS-CoV.
Methods
This analysis included cases admitted between January 2014 and December 2017. The included patients had a minimum of 3 nasopharyngeal MERS-CoV RT-PCR tests for confirmation and needed 2 negative samples for MERS-CoV evaluated 48 hours apart with clinical improvement or stabilization apart to ensure clearance.
Results
A total of 408 patients with positive MERS-CoV test results were treated at the referring hospital. We excluded 72 patients who had only 1 swab result available in the system and were treated in the initial years of the disease. Of the remaining 336 patients, 300 (89%) had a positive result after 1 swab, 324 (96.5%) had a positive result after 2 consecutive swabs, and 328 (97.6%) had a positive result after 3 consecutive swabs.
Methods
This analysis included cases admitted between January 2014 and December 2017. The included patients had a minimum of 3 nasopharyngeal MERS-CoV RT-PCR tests for confirmation and needed 2 negative samples for MERS-CoV evaluated 48 hours apart with clinical improvement or stabilization apart to ensure clearance.
Results
A total of 408 patients with positive MERS-CoV test results were treated at the referring hospital. We excluded 72 patients who had only 1 swab result available in the system and were treated in the initial years of the disease. Of the remaining 336 patients, 300 (89%) had a positive result after 1 swab, 324 (96.5%) had a positive result after 2 consecutive swabs, and 328 (97.6%) had a positive result after 3 consecutive swabs.
Of the total cases, 46 (13.7%) had a positive MERS-CoV test then a negative test, followed by positive test results.
Conclusions
Our data indicate that 2 to 3 nasopharyngeal samples are needed to produce the highest yield of positive results for MERS-CoV. In addition, 2 negative results 48 hours apart with clinical improvement or stabilization are needed to clear patients from MERS-CoV. Evaluation of the yield of sputum samples is needed to assess the effectiveness against nasopharyngeal swabs.
The most common (and least invasive) sampling method for respiratory infections - and the only one cited in this abstract - is via Nasophyaryngeal (NP) swab. Mentioned in the conclusion, however, is the need to evaluate the comparative effectiveness of sputum samples. Conclusions
Our data indicate that 2 to 3 nasopharyngeal samples are needed to produce the highest yield of positive results for MERS-CoV. In addition, 2 negative results 48 hours apart with clinical improvement or stabilization are needed to clear patients from MERS-CoV. Evaluation of the yield of sputum samples is needed to assess the effectiveness against nasopharyngeal swabs.
The CDC's interim recommendations for specimen collection for MERS are more rigorous, calling for `Collection of all three specimen types (not just one or two of the three), lower respiratory, upper respiratory and serum specimens for testing using the CDC MERS rRT-PCR assay is recommended. '
You'll find the CDC's recommendations at the link below.Inconsistent MERS test results could be the result of a number of factors, including: sub-optimal specimen collection, sensitivity issues with the laboratory test, or perhaps variations in viral shedding by the patient over time.In October of 2015, we saw one of South Korea's 180+ MERS patients relapse, and be put back into isolation, two weeks after being released from the hospital (see Korean Govt. Statement On MERS Patient `Relapse and Isolation).
While this is the only documented relapse with MERS I'm aware of, I imagine few are retested after leaving the hospital. We have seen patients with other infections - including Ebola & Zika - continue to harbor (and shed) viruses long after testing negative.A subtle reminder that while `no' should always mean no - sadly - for lab tests, it isn't always so.
http://afludiary.blogspot.com/2018/1...sting-for.html