A touchdown nucleic acid amplification protocol as an alternative to culture backup for immunofluorescence in the routine diagnosis of acute viral respiratory tract infections.
BACKGROUND
Immunofluorescence and virus culture are the main methods used to diagnose acute respiratory virus infections. Diagnosing these infections using nucleic acid amplification presents technical challenges, one of which is facilitating the different optimal annealing temperatures needed for each virus. To overcome this problem we developed a diagnostic molecular strip which combined a generic nested touchdown protocol with in-house primer master-mixes that could recognise 12 common respiratory viruses.


RESULTS
Over an 18 month period a total of 222 specimens were tested by both immunofluorescence and the molecular strip. The specimens came from 103 males (median age 3.5 y), 80 females (median age 9 y) and 5 quality assurance scheme specimens. Viruses were recovered from a number of specimen types including broncho-alveolar lavage, nasopharyngeal secretions, sputa, post-mortem lung tissue and combined throat and nasal swabs. Viral detection by IF was poor in sputa and respiratory swabs. A total of 99 viruses were detected in the study from 79 patients and 4 quality control specimens: 31 by immunofluorescence and 99 using the molecular strip. The strip consistently out-performed immunofluorescence with no loss of diagnostic specificity.


CONCLUSIONS
The touchdown protocol with pre-dispensed primer master-mixes was suitable for replacing virus culture for the diagnosis of respiratory viruses which were negative by immunofluorescence. Results by immunofluorescence were available after an average of 4-12 hours while molecular strip results were available within 24 hours, considerably faster than viral culture. The combined strip and touchdown protocol proved to be a convenient and reliable method of testing for multiple viruses in a routine setting.
Coyle
Peter V
PV
Regional Virus Laboratory, Royal Hospitals Trust, Belfast, BT12 6BA, UK. peter.coyle@bll.n-i.nhs.uk
Ong
Grace M
GM
O'Neill
Hugh J
HJ
McCaughey
Conall
C
De Ornellas
Dennis
D
Mitchell
Frederick
F
Mitchell
Suzanne J
SJ
Feeney
Susan A
SA
Wyatt
Dorothy E
DE
Forde
Marian
M
Stockton
Joanne
J
D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D017931:DNA Primers; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction / Q000379:methods*; D012141:Respiratory Tract Infections / Q000175:diagnosis*; D014776:Virus Cultivation; D014777:Virus Diseases / Q000175:diagnosis*; D014780:Viruses / Q000235:genetics / Q000302:isolation & purification
D017931:DNA Primers