Advanced Techniques in Diagnostic Microbiology

38 S. Campbell and M. L. Landry
Rapid diagnosis of malaria by antigen detection is a promising approach to field
diagnosis. The proliferation of chloroquine-resistant strains and the expense of
newer antimalarial drugs may make these tests economical in endemic regions.
Tests are available for Plasmodium falciparum and Plasmodium vivax.
Rapid antigen tests have also been evaluated for Wuchereria bancrofti infections.
They appear to be more sensitive than direct microscopy and approach or exceed
the sensitivity of concentration techniques in some studies (Chandrasena et al.,
2002).
Viruses
Hospitals that serve infants and children have long provided rapid antigen testing
for respiratory syncytial virus (RSV) and rotavirus (Wilhelmi et al., 2001; Slinger
et al., 2004). Recently, testing for influenza using membrane EIA or other rapid
formats has increased in clinics, emergency departments, and hospitals in highrisk
adults and in pediatric patients. Having a test result available within 15 to
30 min has been shown to reduce use of antibiotics and other tests and to allow
administration of antiviral agents when needed (Barenfanger et al., 2000; Bonner
et al., 2003). Antigen tests are the only methods that can currently provide such
rapid results, and the number of commercial rapid influenza tests has increased
dramatically (Storch, 2003). Some detect only influenza A, whereas others detect
both A and B but may not differentiate between them. Although less sensitive than
cell culture or IF, these tests perform very well in young children because children
shed high titers of virus. There is concern however that the simpler and more rapid
tests are less specific, and false positives have been reported.
IF is slower than other rapid antigen tests but has advantages of a broader array
of analytes available, ability to multiplex and ability to quantitate infected cells.
Because IF is commonly done in virology laboratories for identification of culture
isolates, the equipment and expertise are usually available. Obtaining excellent
results using IF directly on clinical samples, however, requires a significant commitment
to training, monitoring, and quality control. Performance characteristics
must be established in each laboratory, usually by comparing IF results with culture
results. Without careful attention to detail and extensive training, nonspecific
staining can be misinterpreted as positive, or small numbers of positive cells can
be overlooked. Use of cytocentrifugation to prepare slides enhances slide quality
and test sensitivity.
Respiratory virus screening by use of pooled antibodies can test for 7 viruses in
a single cell spot (Landry and Ferguson, 2000b). Because the same symptoms can
be caused by many viruses, this provides an advantage similar to culture. Likewise,
antibodies to herpes simplex virus (HSV) and varicella-zoster virus (VZV) can be
pooled to screen skin lesions (Scicchitano et al., 1999).
The use of IF to rapidly detect and quantitate cytomegalovirus (CMV) in peripheral
blood revolutionized the diagnosis and monitoring of CMV infections,
especially in transplant patients (Gerna et al., 1992). Even with the increasing
use of polymerase chain reaction (PCR) to monitor viral load, CMV antigenemia