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Volume 17, Number 2—February 2011

Dispatch

Comparison of Pandemic (H1N1) 2009 and Seasonal Influenza Viral Loads, Singapore

Chun K. Lee, Hong K. Lee, Tze P. Loh, Florence Y.L. Lai, Paul A. Tambyah, Lily Chiu, Evelyn S.C. Koay, and Julian W. TangComments to Author 
Author affiliations: Author affiliations: National University Hospital, Singapore (C.K. Lee, H.K. Lee, T.P. Loh, P.A. Tambyah, L. Chiu, E.S.C. Koay, J.W. Tang); Ministry of Health, Singapore (F.Y.L. Lai); National University of Singapore, Singapore (P.A. Tambyah, E.S.C. Koay)

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Table 2

Analysis of pandemic (H1N1) 2009 (HA and NP) and seasonal H3 (MP) viral loads with clinical parameters, Singapore, May–November 2009*

Characteristic Pandemic influenza
Seasonal H3 influenza
No. HA viral load, log10 copies/mL, mean (SD) NP viral load, log10 copies/mL, mean (SD) MANOVA
p value† No. MP viral load, log10 copies/mL, mean (SD) ANOVA
p value
Time from symptom onset, d <0.0001 0.0223
1–2 416 6.49 (1.44) 6.49 (1.38) 53 8.12 (1.43)
3–4 114 6.18 (1.39) 6.16 (1.40) 20 7.27 (1.31)
5–7
48
5.33 (1.21)
5.31 (1.23)


4
6.76 (1.22)

Age, y 0.0112‡ 0.9652‡
0–4 69 6.46 (1.40) 6.45 (1.39) 7 7.66 (0.75)
5–14 144 6.62 (1.36) 6.65 (1.26) 11 7.93 (1.38)
15–34 250 6.34 (1.48) 6.33 (1.43) 28 7.88 (1.66)
35–54 72 5.85 (1.46) 5.88 (1.41) 13 7.99 (1.04)
>55
43
5.88 (1.41)
5.83 (1.50)


18
7.63 (1.66)

Sex 0.3018‡ 0.3883‡
F 275 6.23 (1.49) 6.26 (1.38) 41 7.68 (1.52)
M
303
6.42 (1.41)
6.39 (1.43)


36
8.00 (1.35)

Comorbidities 0.9967‡ 0.0249‡
Yes 262 6.35 (1.49) 6.35 (1.44) 22 7.23 (1.53)
No
316
6.31 (1.42)
6.31 (1.39)


55
8.07 (1.35)

Clinical severity§
Severe 23 5.97 (1.76) 5.98 (1.84)
Hospitalized 222 6.44 (1.49) 6.42 (1.43) 7.55 (1.06)
Outpatient 229 6.29 (1.45) 6.30 (1.40) 19 7.25 (1.54)

*HA, hemagglutinin; NP, nucleoprotein; MP, matrix protein; MANOVA, multiple analysis of variance; ANOVA, analysis of variance.
†Wilks Lambda statistics.
‡Effect of days from symptom onset adjusted.
§Analysis included patients who sought care during the mitigation phase only (n = 474 for pandemic and n = 26 for H3 seasonal influenzas). Singapore switched from premitigation (i.e., containment) to mitigation management protocols on July 8, 2009, which altered how patient treatment with oseltamivir was initiated. However, this transition does not affect the results shown above because none of the patients were undergoing treatment when these first diagnostic samples were taken.
¶Includes 1 severe case.

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