The significance of an antigenic relationship between H1N1 viruses was shown in a similar inverse correlation with the titer of antibody to the most recently preceding seasonal A/H1N1 virus

The significance of an antigenic relationship between H1N1 viruses was shown in a similar inverse correlation with the titer of antibody to the most recently preceding seasonal A/H1N1 virus. All health center visits are coded; codes used for possible influenza were codes that correlate with proven influenza [20]. Also shown is the number of specimens that tested positive for influenza A in rapid diagnostic tests at the clinic or in RT-PCR tests from subjects reporting an ARI. As shown, the pH1N1 epidemic was ongoing among students during the enrollment period (weeks 37C39); no other influenza virus was detected during surveillance. The epidemic peaked in a 4-week period in late September and early October (weeks 37C40); illnesses caused by pH1N1 virus continued at a low level throughout the remaining surveillance period. Open in a separate window Figure 1. The 2009 2009 influenza A(H1N1) epidemic at Texas A&M University. Abbreviation: ARI, acute respiratory illness. Study Illnesses Seventy-six subjects with 77 illnesses reported to the study site with a moderate or severe ARI during the surveillance period. Sixty-three (82%) of these illnesses yielded a virus; 24 were pH1N1 influenza virus, 22 rhinovirus, 7 both pH1N1 and rhinovirus, 1 rhinovirus and HKU1 coronavirus, 4 coronavirus (2 HKUI, 1 229E, 1 nicein-125kDa NL63), 2 enterovirus, 1 respiratory syncytial virus, and 2 herpes simplex virus, and 14 were negative. During the peak of pH1N1 infections, less than half of the illnesses yielded pH1N1. Mean quantity of infectious influenza virus in respiratory secretion samples of 29 subjects on visit days 1, 3, 5, and 7 is shown in Table 1. Mean virus titer at presentation was 40 000 (104.6) median tissue culture infective dose (TCID50)/mL of specimen. The mean titer was only 80 TCID50 2 days later and 10 at the day 5 and day 7 visits. Eighteen of these subjects were given zanamivir as treatment (day 1 or day 2 of illness) and 11 were not (physician decision). Mean titers at presentation were higher for those treated (105.3 vs 104.0), but the means were not significantly different (MannCWhitney test). Titers were low at subsequent visits and did not differ; similarly, the means between day 1 and day 3 for those treated and not treated did not differ. A comparison of illnesses among subjects infected with pH1N1 influenza, a rhinovirus, or both is shown in Table 1. At presentation, fever (100F) was more common among subjects with influenza (RXC contingency, .001). For mean symptom severity scores, myalgia scores were greater for influenza; rhinorrhea scores were greater for rhinovirus infections (= .01 and .01, respectively; MannCWhitney test). Myalgias and rhinorrhea were also different among the 3 groups (= .02 and = .01, respectively, KruskalCWallis test). Rhinorrhea persisted as a major symptom for rhinovirus-infected subjects for the 7 days of observation. Correlations With pH1N1 Antibody Occurrences of pH1N1 influenza infections and illnesses in relation to serum HAI antibody titer at enrollment are shown in Table 2. One hundred twenty-two (23.0%) subjects exhibited a significant antibody response to pH1N1 between enrollment (September 2009) and spring follow-up (March 2010). One hundred eighty-eight (37%) had serum antibody (1:8) to pH1N1 virus Butoconazole at enrollment. There was an inverse correlation between baseline serum antibody titer to pH1N1 virus and occurrence of pH1N1 infection Butoconazole during the surveillance period (2 for trend, .001). Thirty-one symptomatic influenza infections among enrolled subjects were detected, 30 by virus and serologic tests and 1 by serologic tests only. The apparent inverse correlation for infection and illness among those enrolled with ARI was not significant. Forty-five retrospectively identified ARIs were considered moderate Butoconazole to severe; pH1N1 infection was detected in 14 of 19 (74%) subjects with probable influenza, 4 of 9 (44%) subjectswith possible influenza, and 2 of 17 (12%) subjects not designated to have clinical influenza (the clinical diagnosis for the 2 2 was a severe cold). When the retrospectively identified Butoconazole moderate to severe ARIs with a significant antibody response were included, the inverse correlation between baseline titer and frequency of pH1N1 infection and illness was significant (2 for trend, = .01). Table 2. Frequency of 2009 Butoconazole H1N1 Infections and Illnessesa in.