112 Diagnostic Tests

Chapter 7: Diagnostic Tests

Wolfgang Preiser, Christian Drosten

Introduction

Despite the initial rapid progress in the discovery of the causative agent (see Chapter 2: Virology) and the early development of diagnostic tests, further progress in the establishment of laboratory tests for SARS has been slower than originally expected.

While various molecular (PCR-based) assays have been developed by different groups around the world, and although one such assay is available commercially, results of these tests should still not be used to rule out a suspected case of SARS, according to current WHO recommendations.

The continual lack of a rapid laboratory test to aid the diagnosis of suspected cases of SARS makes this area a priority for further research efforts (WHO, Update 71).

In many viral diseases, virus shedding is greatest during the early symptomatic phase, i.e. around, and immediately following the onset of symptoms. Unfortunately, virus excretion is comparatively low during the initial phase of SARS. It peaks in respiratory specimens and in stools at around day 10 after the onset of the clinical illness. In order to make an early diagnosis, it is therefore necessary to use highly sensitive tests that are able to detect the low levels of viral genome present during the first days of illness.

Because presently available tests are not generally able to detect the small amounts of SARS coronavirus (SARS-CoV) initially shed, they do not yet play a role in patient management and case control, as SARS patients may be capable of infecting others during the initial phase and therefore need to be reliably detected and quickly isolated (WHO, Update 71).

The results of the first clinical studies on SARS are now available and able to shed light on the clinical usefulness of various tests on different patient samples at different time points. In one series, IgG seroconversion was documented in 93% of patients at a mean of 20 days;

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