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Pandemic and Seasonal Flu in Singapore Have Different Symptom Patterns
Laurie Barclay, MD
Authors and Disclosures
May 24, 2010 — Pandemic and seasonal flu in Singapore have different symptom patterns, according to the results of a large prospective study reported in the May 24 issue of the Archives of Internal Medicine.
"Singapore is a tropical country with a temperature range of 23°C to 35°C and relative humidity of 48% to 100% throughout the year," write Julian Wei-Tze Tang, PhD, MRCP, MRCPath, from National University of Singapore, and colleagues. "Influenza incidence peaks in June through July and November through January, though influenza cases can be detected throughout the year."
For enhanced influenza surveillance between May 1 and July 28, 2009, a novel dual-gene diagnostic polymerase chain reaction assay was specifically designed to target the hemagglutinin and nucleoprotein genes of the new influenza A (H1N1/2009) virus. This assay used nasopharyngeal swabs collected from symptomatic patients, their close contacts, and travelers returning from areas affected by influenza A (H1N1/2009) who presented to the main hospital emergency department and to affiliated primary care clinics.
The pandemic influenza A (H1N1/2009) displaced and then replaced the seasonal influenzas (H3N2, H1N1, and B) from the week of June 16 to June 23, 2009. There were 2683 samples tested during the 12-week surveillance period of the study. Of these samples, 742 (27.6%) were positive for any influenza virus, using the rapid detection assay, including 547 cases of influenza A (H1N1/2009) (20.4%), 167 of influenza A (H3N2) (6.2%), 14 of influenza A (H1N1) (0.5%), and 12 of influenza B (0.4%).
These groups differed significantly in age (P < .001), fever (P < .001), cough (P < .001), sore throat (P = .002), rhinorrhea (P = .001), and dyspnea (P < .001), based on multivariate analysis.
Pandemic influenza was associated with cough in 88.1% of patients, fever in 79.3%, sore throat in 53.7%, and rhinorrhea in 49.9%. For the predominant strain of seasonal influenza, the most common symptoms were fever in 88%, cough in 81.4%, rhinorrhea in 55.7%, and sore throat in 38.3% of patients.
"From this large prospective study, there was a lower incidence of fever and dyspnea in patients with pandemic influenza A(H1N1/2009) infection," the study authors write. "Similar to reports from elsewhere, it was also found that this pandemic virus tends to infect younger people, though with fewer symptoms, on average, than seasonal influenza. Early pandemic influenza A(H1N1/2009) infections appeared to be slightly milder than seasonal influenza as indicated by different symptom patterns in the presentation of more than 500 cases of influenza A(H1N1/2009) during April through July to a large teaching hospital in Singapore."
Limitations of this study include sole reliance on the requesting physician to accurately complete the influenza surveillance forms, sample bias toward symptomatic patients, lack of clinical data regarding diabetes or other clinical risk factors, and failure to analyze separately the symptom patterns of specific ethnic groups.
"It is likely that these symptom patterns will continue to evolve and change as the novel pandemic influenza A(H1N1/2009) eventually predominates, globally, in the susceptible human population," the study authors conclude. "However, this early window period in this first wave of the pandemic has provided an opportunity to compare the symptomatology of these different influenza viruses in this particular tropical environment and ethnically diverse population during this transitional period."
One of the study authors has received research support from Baxter and Adamas and honoraria from Novartis and has served on the board of the Asia Pacific Advisory Council of Influenza. Another study author is supported by the H1N1 Advance Urgent Funds from the Yong Loo Lin School of Medicine, National University of Singapore.
Arch Intern Med. 2010;170:861-867.
http://www.medscape.com/viewarticle/722294
link to abstract: http://archinte.ama-assn.org/cgi/content/abstract/170/10/861
Pandemic and Seasonal Flu in Singapore Have Different Symptom Patterns
Laurie Barclay, MD
Authors and Disclosures
May 24, 2010 — Pandemic and seasonal flu in Singapore have different symptom patterns, according to the results of a large prospective study reported in the May 24 issue of the Archives of Internal Medicine.
"Singapore is a tropical country with a temperature range of 23°C to 35°C and relative humidity of 48% to 100% throughout the year," write Julian Wei-Tze Tang, PhD, MRCP, MRCPath, from National University of Singapore, and colleagues. "Influenza incidence peaks in June through July and November through January, though influenza cases can be detected throughout the year."
For enhanced influenza surveillance between May 1 and July 28, 2009, a novel dual-gene diagnostic polymerase chain reaction assay was specifically designed to target the hemagglutinin and nucleoprotein genes of the new influenza A (H1N1/2009) virus. This assay used nasopharyngeal swabs collected from symptomatic patients, their close contacts, and travelers returning from areas affected by influenza A (H1N1/2009) who presented to the main hospital emergency department and to affiliated primary care clinics.
The pandemic influenza A (H1N1/2009) displaced and then replaced the seasonal influenzas (H3N2, H1N1, and B) from the week of June 16 to June 23, 2009. There were 2683 samples tested during the 12-week surveillance period of the study. Of these samples, 742 (27.6%) were positive for any influenza virus, using the rapid detection assay, including 547 cases of influenza A (H1N1/2009) (20.4%), 167 of influenza A (H3N2) (6.2%), 14 of influenza A (H1N1) (0.5%), and 12 of influenza B (0.4%).
These groups differed significantly in age (P < .001), fever (P < .001), cough (P < .001), sore throat (P = .002), rhinorrhea (P = .001), and dyspnea (P < .001), based on multivariate analysis.
Pandemic influenza was associated with cough in 88.1% of patients, fever in 79.3%, sore throat in 53.7%, and rhinorrhea in 49.9%. For the predominant strain of seasonal influenza, the most common symptoms were fever in 88%, cough in 81.4%, rhinorrhea in 55.7%, and sore throat in 38.3% of patients.
"From this large prospective study, there was a lower incidence of fever and dyspnea in patients with pandemic influenza A(H1N1/2009) infection," the study authors write. "Similar to reports from elsewhere, it was also found that this pandemic virus tends to infect younger people, though with fewer symptoms, on average, than seasonal influenza. Early pandemic influenza A(H1N1/2009) infections appeared to be slightly milder than seasonal influenza as indicated by different symptom patterns in the presentation of more than 500 cases of influenza A(H1N1/2009) during April through July to a large teaching hospital in Singapore."
Limitations of this study include sole reliance on the requesting physician to accurately complete the influenza surveillance forms, sample bias toward symptomatic patients, lack of clinical data regarding diabetes or other clinical risk factors, and failure to analyze separately the symptom patterns of specific ethnic groups.
"It is likely that these symptom patterns will continue to evolve and change as the novel pandemic influenza A(H1N1/2009) eventually predominates, globally, in the susceptible human population," the study authors conclude. "However, this early window period in this first wave of the pandemic has provided an opportunity to compare the symptomatology of these different influenza viruses in this particular tropical environment and ethnically diverse population during this transitional period."
One of the study authors has received research support from Baxter and Adamas and honoraria from Novartis and has served on the board of the Asia Pacific Advisory Council of Influenza. Another study author is supported by the H1N1 Advance Urgent Funds from the Yong Loo Lin School of Medicine, National University of Singapore.
Arch Intern Med. 2010;170:861-867.
http://www.medscape.com/viewarticle/722294
link to abstract: http://archinte.ama-assn.org/cgi/content/abstract/170/10/861
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