Short communicationPerformance of laboratory diagnostics for the detection of influenza A(H1N1)v virus as correlated with the time after symptom onset and viral load
Section snippets
Background
The current outbreak of novel influenza A (H1N1)v virus [henceforth: influenza A(H1N1)v virus, where v stands for variant, as proposed by the World Health Organization] was first detected in Mexico in late March 2009 and spread worldwide rapidly. The first case in Hong Kong was detected in a visitor from Mexico on May 1, 2009. The infection continued to be introduced by overseas visitors/returnees for over 1 month when the first local outbreak occurred on June 10, 2009.
Objectives
We compared the performance of RAT, viral culture and RT-PCR tests for the detection of influenza A(H1N1)v virus and correlated the sensitivity with the time after symptom onset among patients diagnosed as having influenza A(H1N1)v infection.
Clinical specimens
Nasopharyngeal aspirate (NPA), combined throat and nasal swabs (TNS) nasopharyngeal swabs (NPS) and throat swabs (TS) were obtained from individuals fulfilling both the clinical and epidemiological criteria for suspected influenza A(H1N1)v infection.1 Specimens were placed in viral transport media and transported to the laboratory within 24 h after collection.
Data collection
Influenza A(H1N1)v virus infection was made notifiable disease on April 27, 2009 in Hong Kong. All patients admitted to hospital with
Patient descriptions
During the first 8 weeks of influenza A(H1N1)v outbreak, 5740 patients were tested and 596 patients were diagnosed as having influenza A(H1N1)v infection with a positive result on viral culture and/or RT-PCR assays. Information on date of symptom onset was available for 587 of these patients. They ranged in age from 5 months to 70 years, 60% were in the age group between 11 and 20 years and 99% were younger than 60 years, the mean age of patients was 21 years. Respiratory samples comprised 229
Discussion
Our data show, for the first time, comparison of RAT, viral culture and RT-PCR for the detection of A(H1N1)v as correlated with time after symptom onset and viral load. In the present study, influenza A(H1N1)v virus replicated well in MDCK cells producing cytopathic effect (CPE) as early as 2 days after inoculation, with an average of 3.5 days after inoculation (N = 551; confidence interval, CI = 3.4–3.6), much earlier than influenza A(H1N1) and A(H3N2) viruses that took 5.2 days (N = 47; CI = 4.7–5.7)
Conflicts of interest
None.
Acknowledgements
We thank all staff of the Virology Division, Public Health Laboratory Services Branch, and Surveillance and Epidemiology Branch, Centre for Health Protection, for technical assistance and epidemiological information.
References (15)
- et al.
Analytical sensitivity of rapid influenza antigen detection tests for swine-origin influenza virus (H1N1)
J Clin Virol
(2009) - et al.
Performance of six influenza rapid tests in detecting human influenza in clinical specimens
J Clin Virol
(2007) - Centre for Health Protection. Reporting criteria for suspected human swine influenza....
- et al.
Influenza
- Centre for Health Protection. CHP molecular diagnostic protocols for the detection of human swine influenza virus type...
- World Health Organization. WHO Information for Laboratory Diagnosis of New Influenza A (H1N1) Virus in Humans. 21 May...
- et al.
Testing of diagnostic methods for detection of influenza virus for optimal performance in the context of an influenza surveillance network
J Clin Microbiol
(2007)