Skip Navigation

Notes from the Field: Outbreak of 2009 Pandemic Influenza A (H1N1) Virus at a Large Public University in Delaware, April-May 2009

  1. A. Danielle Iuliano1,
  2. Carrie Reed1,
  3. Alice Guh1,
  4. Mitesh Desai1,
  5. D. L. Dee1,
  6. Preeta Kutty1,
  7. L. Hannah Gould1,
  8. Mark Sotir1,
  9. Gavin Grant1,
  10. Michael Lynch1,
  11. Tarissa Mitchell1,
  12. Jane Getchell3,
  13. Bo Shu1,
  14. J Villanueva1,
  15. Stephen Lindstrom1,
  16. Mehran S. Massoudi1,
  17. Joseph Siebold2,
  18. Paul R. Silverman3,
  19. Gregory Armstrong1, and
  20. David L. Swerdlow1
  1. 1Centers for Disease Control and Prevention, Atlanta, Georgia
  2. 2University of Delaware, Newark, Division of Public Health, Dover
  3. 3Delaware Health and Social Services, Division of Public Health, Dover
  1. Reprints or correspondence: Dr A. Danielle Iuliano, 1600 Clifton Rd, MS E-45, Atlanta, GA 30333 (Aoi0{at}cdc.gov).
 
Next Section

Abstract

Background. In late April 2009, the first documented 2009 pandemic influenza A (pH1N1) virus infection outbreak in a university setting occurred in Delaware, with large numbers of students presenting with respiratory illness. At the time of this investigation, little was known about the severity of illness, effectiveness of the vaccine, or transmission factors of pH1N1 virus infection. We characterized illness, determined the impact of this outbreak, and examined factors associated with transmission.

Methods. Health clinic records were reviewed. An online survey was administered to all students, staff, and faculty to assess influenza-like illness (ILI), defined as documented or subjective fever with cough or sore throat.

Results. From 26 April–2 May 2009, the health clinic experienced a sharp increase in visits for respiratory illness, with 1080 such visits among a total of 1430 student visits, and then a return to baseline visit levels within 2 weeks. More than 500 courses of oseltamivir were distributed, and 24 cases of influenza A (pH1N1) virus infection were confirmed. Of 29,000 university students and faculty/staff, 7450 (30%) responded to the survey. ILI was reported by 604 (10%) of the students and 73 (5%) of the faculty/staff. Travel to Mexico (relative risk [RR], 2.9; 95% confidence interval [CI], 1.8–4.7) and participation in “Greek Week” activities (RR, 2.2; 95% CI, 1.8–2.8) were associated with ILI. Recipients of the 2008–2009 seasonal influenza vaccine had the same risk of ILI as nonrecipients (RR, 1.0). Four (3%) of the students with ILI were hospitalized; there were no deaths.

Conclusions. pH1N1 spread rapidly through the University of Delaware community with a surge in illness over a 2-week period. Although initial cases appear to be associated with travel to Mexico, a rapid increase in cases was likely facilitated by increased student interactions during Greek Week. No protective effect from receiving seasonal influenza vaccine was identified. Although severe illness was rare, the outbreak caused a substantial burden and challenge to the university health care system. Preparedness efforts in universities and similar settings should include enhancing health care surge capacity.

Human infection with 2009 pandemic influenza A (H1N1) virus (pH1N1) was first identified in the United States on 15 April 2009 and is characterized by a combination of gene segments not previously identified [1]. On 27 April 2009, the University of Delaware Student Health Service (UDSHS) observed an unexpected increase in the number of students seeking care for a respiratory illness, and within 2 days, >600 students complaining of respiratory symptoms visited the clinic, overwhelming the campus health system. On 30 April, the first pH1N1 cases on campus were confirmed by the Centers for Disease Control and Prevention (CDC).

The University of Delaware (UD) campus in Newark has a student population of 19,000 graduate and undergraduate students, with 30% living in on-campus residence halls [2, 3], and ∼17% are members of a fraternity or sorority (Panhellenic organization) [4]. The UD spring semester was 9 February–20 May 2009, and spring break occurred from 27 March–5 April 2009. Panhellenic organizations held their annual “Greek Week” from 20–25 April 2009, which is a campus-wide event that includes social and athletic events open to all students. The UDSHS is located on-campus and provides health care to students. Before this outbreak, the most recent case of seasonal influenza A had occurred on 16 March, and the most recent case of influenza B had occurred on 10 April.

At the time of this investigation, the transmissibility and health impact of pH1N1, disease severity, age distribution of patients, and the effectiveness of seasonal influenza vaccine were largely unknown. The objectives of this investigation were to better understand and characterize the illness, the epidemiology of infection, the severity of illness, effectiveness of 2008–2009 seasonal influenza vaccine, the use of community mitigation measures, and the impact of pH1N1 virus infection during the first documented university outbreak of pH1N1 in the United States.

Previous SectionNext Section

Methods

Chart abstraction. We reviewed UDSHS visits and discharge diagnoses for 1 February–8 May 2009 and calculated the number of visits for respiratory illness, defined using International Classification of Diseases, 9th Revision , discharge diagnosis for upper and/or lower respiratory infection, influenza, otitis media, respiratory failure, respiratory distress, asthma or chronic obstructive pulmonary disease, fever, pneumonia, pharyngitis, laryngitis, sore throat, rhinorrhea, or cough. To characterize clinical illness among students who presented for care at UDSHS prior to and during the outbreak, electronic medical records for all respiratory illness visits from 5 April–8 May 2009 were reviewed, and information was extracted to determine the presence of acute febrile respiratory illness (AFRI), defined as documented (temperature, ⩾37.8°C) or subjective fever (chills or sweats) with at least one of the following: cough, sore throat, nasal congestion, or rhinorrhea. Chart abstractions were completed for students with confirmed pH1N1 infection, a randomly selected subset of 50% of students with AFRI, and 25% of students with nonfebrile respiratory illness. A standard form that included demographic data and illness characteristics was used for chart abstraction. We characterized influenza-like illness (ILI) (documented or subjective fever plus cough or sore throat) among those with AFRI.

Online survey. A cross-sectional survey to describe the extent of the outbreak and burden of illness among students, staff, and faculty and to assess health-seeking behaviors, influenza vaccination status, possible risk factors for illness, prevention practices, and adherence to prevention measures during the period 27 March–9 May 2009 was conducted online from 10 May through 18 May 2009. The confidential survey was administered using mrInterview software, version 4.5 (SPSS). Email invitations and reminders were sent to the university community.

Respondents were classified as having an acute respiratory illness (ARI) defined as fever, cough, sore throat, or nasal (congestion or rhinorrhea) and/or ILI during the period 27 March–9 May 2009. We calculated attack rates, relative risks (RR), and 95% confidence intervals (CIs) for ARI and ILI. We compared symptoms and patient characteristics for respondents with ILI and those with ARI to characterize the spectrum and severity of illness seen at the University during the outbreak. In addition, the risk of ILI was compared between potential risk factors for ILI, such as age, behavioral factors, and underlying health conditions. Analyses were performed using SAS statistical software, version 9.2.

Previous SectionNext Section

Results

Description of the outbreak. Nasopharyngeal (NP) swab samples from 4 students that were collected on 27 April 2009 had results positive for influenza A virus obtained with a rapid influenza diagnostic test (QuickVue) but were unsubtypable at the Delaware Division of Public Health Laboratory on 28 April, which was suggestive of pH1N1 infection. On 28 April, the UD administration issued a campus-wide alert notifying students, parents, faculty, and staff of 4 probable cases of pH1N1 virus infection and recommended that persons with respiratory illness visit UDSHS. On 29 April, because of the large increase in students seeking care, the University and the Delaware Health and Social Services (DHSS) Division of Public Health opened a neighborhood emergency health center (NEHC) for students at a campus gymnasium. On the same day, the University began cancelling extracurricular, social, and athletic events but maintained the academic class schedule. The following day, 30 April, the first 4 cases were confirmed as influenza A (pH1N1) virus infection by the CDC laboratory with use of polymerase chain reaction (PCR).

From 26 April–2 May 2009, UDSHS recorded 1430 student visits, of which 1080 (76%) included chief complaints consistent with a respiratory illness. In addition, from 29 April through 30 April, the NEHC clinic evaluated >300 students with respiratory symptoms. During the first week (26 April–2 May), 92 rapid influenza tests were administered at UDSHS; 24 (26%) had results positive for influenza A virus and were sent to the state laboratory for PCR testing. Of the UDSHS rapid test-positive samples, 18 were positive for influenza A virus but unsubtypable at the state laboratory. By 5 May 2009, 24 confirmed cases of H1N1 virus infection were confirmed by the CDC, including 6 in patients who sought care outside of the university. Comparing the peak outbreak week of 26 April–2 May 2009 to the same week in 2008, there were more than twice the number of visits in 2009, compared with 2008 (782 vs 325) (Figure 1). By the following week, 3–9 May 2009, the number of visits to the UDSHS for respiratory symptoms had decreased dramatically. Seventy-five rapid influenza tests were conducted, and 5 (7%) were positive for influenza A virus but were not sent to the state for further testing. Campus activities and events resumed on 3 May, and the number of students with respiratory illness continued to decrease. The last positive rapid influenza test result was reported on 15 May.

Figure 1
View larger version:
Figure 1

University of Delaware Student Health Services visits with diagnoses consistent with respiratory illness, 2008 and 2009.

Because of the volume of students who presented with respiratory complaints, once pH1N1 virus infection was confirmed at the university, laboratory confirmation of positive rapid influenza tests was discontinued. Students were presumptively treated with oseltamivir if they self-reported any respiratory illness with a combination of fever or chills, sore throat, cough, nasal congestion, or runny nose and were seen within 48 h after onset. More than 500 courses of oseltamivir were distributed to students during the period 29 April–1 May 2009.

Clinic data and chart abstraction. Of the 1083 students seen at UDSHS with respiratory illness during the period 5 April–8 May 2009, 509 (47%) had AFRI. Of those with AFRI, charts were abstracted for 258, of whom 237 (92%), including the 24 confirmed pH1N1 cases, met the definition for ILI. Among those with ILI, commonly reported symptoms besides fever included: sore throat (80%), cough (77%), nasal symptoms (68%), and gastrointestinal complaints (19%). Fifty-six (24%) of the students with ILI were tested for influenza at UDSHS. Among those tested, 22 were positive for influenza A virus, including 17 of the patients with confirmed pH1N1 cases; 34 were negative, including 3 of the patients with confirmed pH1N1. The remaining 574 students (53%) who sought care for respiratory illness were afebrile, and reported symptoms included: sore throat (79%), cough (61%), nasal symptoms (63%), and gastrointestinal symptoms (5%). Nine students with afebrile illness were tested for influenza, and all had negative test results.

Online survey response. Electronic invitations for the online survey were sent to 18,872 students and 5871 faculty/staff; 6049 (32%) of the students and 1401 (24%) of the faculty/staff completed the survey. Of student respondents, 66% were female, the median age was 21 years, 13% were Panhellenic organization members, and 40% reported living on campus. By year of study, 27% were seniors, 17% were juniors, 19% were sophomores, 14% were freshmen, and 20% were graduate students. Respondent demographic data including sex, class status, Panhellenic membership, and housing were similar to those for the university overall, except for a higher proportion of women in the survey (66% vs 58% in the university population) [2–4]. Among faculty/staff participants, 63% were female, and 20% were >60 years old.

Descriptive epidemiology and clinical characterization of illness from the survey. Among student respondents, 1545 (26%) reported ARI with onset during the period 27 March–9 May 2009, including 604 (10%) who met the ILI case definition (Figure 2). Of those with ILI, 453 (75%) were women, and 261 (43%) resided on campus. The median duration of illness was 6 days (interquartile range [IQR], 4–9 days). Compared with students with ARI, those with ILI were more likely to report nausea or vomiting, diarrhea, muscle/joint aches, headache, fatigue, and difficulty breathing, but they were as likely to report nasal congestion or rhinnorhea (Table 1). Six students with ARI reported that they stayed overnight in inpatient facilities; 4 of these had ILI. Additional interviews for 4 patients who reported an overnight stay indicated that time of stay was <24 h; 2 stayed overnight at UDSHS infirmary, and 2 stayed in the hospital emergency room.

Figure 2
View larger version:
Figure 2

Reported influenza-like illness (n p 604) among students, by date of onset from online H1N1 survey, University of Delaware, April–May 2009. NEHC, neighborhood emergency health center.

Figure 3
View larger version:
Figure 3

Daily rate of new onset of influenza-like illness per 1000 students by date of onset and participation in Greek Week activities (20–24 April) from H1N1 online survey, University of Delaware, 2009.

Table 1
View larger version:
Table 1

Comparison of 1545 Students with Influenza-Like Illness (ILI) and Non-ILI Respiratory Illness from 27 March through 9 May 2009 Who Responded to H1N1 Influenza Survey

Of the 1401 faculty/staff who responded to the online survey, 194 (14%) reported ARI, and of these, 73 (5%) had ILI. Fifty-one (70%) of the respondents with ILI were female, 20 (27%) were 30–39 years old, 27 (42%) were 50–59 years old, and 10 (14%) were ⩾60 years old. Compared with faculty/staff with ARI (Table 2), those with ILI were more likely to report nausea or vomiting, muscle/joint aches, headache, and fatigue but were as likely to report nasal congestion or rhinnorhea and diarrhea. The median duration of illness for faculty/staff with ILI was 6.5 days (IQR, 4–12.5 days). No hospitalizations were reported among faculty/staff.

Table 2
View larger version:
Table 2

Comparison of 194 Faculty or Staff with Influenza-Like Illness (ILI) and Non-ILI Respiratory Illness Who Responded to H1N1 Influenza Survey

We estimated the number of students and faculty/staff who may have experienced ILI during the outbreak using online survey data. Using the attack rate of ILI (students, 10%; faculty/staff, 5%) along with the size of the community (students, 18,872; faculty/staff, 5871), we estimated that 1887 students and 300 faculty/staff may have had ILI during the outbreak. No deaths were reported among the University community.

A total of 359 (60%) of the student respondents and 40 (49%) of the faculty/staff respondents with ILI indicated visiting a health care provider for their illness at UDSHS or elsewhere. Among students, 123 (37%) reported being tested for influenza, 66 (20%) reported receiving a diagnosis of influenza via testing or presumptive illness characterization by their health care provider, and 119 (33%) were prescribed oseltamivir. Among faculty/staff, 10 (30%) reported being tested for influenza, 4 (12%) were given a diagnosis of influenza, and 6 (17%) were prescribed oseltamivir. The median time from illness onset to treatment was 2 days (IQR, 1–3). Of respondents who sought health care, 129 (36%) of the students and 9 (25%) of the faculty/staff with ILI said that media attention about pH1N1 influenced their decision to seek care. Missing school or work was reported by 361 (61%) of the students (median duration, 2 days; IQR, 1–3 days) and 42 (58%) of the faculty/staff (median duration, 2 days; IQR, 2–3 days).

Compared with 63 (24%) of the students with ARI, 192 (54%) of the students with ILI were more likely to report following advice to stay home until well (Table 1). Following advice to cover coughs or sneezes was reported by 259 (72%) of the students with ILI and 164 (61%) of the students with ARI. While sick, 196 (33%) of the students with ILI reported having someone visit them, compared with 228 (24%) of the students with ARI. Among faculty/staff, differences in adherence to recommendations to reduce the risk of illness transmission were not statistically significant (Table 2).

Epidemiology of illness. Undergraduate students (RR, 2.3; 95% CI, 1.8–3.0) had a higher risk of ILI, but graduate students had a similar risk of ILI (RR, 1.1; 95% CI, 0.8–1.5) compared with faculty/staff (Table 3). Risk of ILI decreased significantly as age increased and was associated with female sex (RR, 1.5; 95% CI, 1.3–1.9). The risk of ILI was similar among students living on or off campus (RR, 1.2; 95% CI, 1.0–1.4). Underlying chronic health conditions were reported by 193 (10%) of respondents with ILI, and the risk of ILI was similar for those with and those without chronic health conditions. Receiving the 2008–2009 seasonal influenza vaccine was reported by 1931 (27%) of the respondents, including 173 (27%) with ILI; 92% received inactivated vaccine. There was no difference in risk of ILI among those who received the vaccine, compared with those who did not (RR, 1.0). After adjusting for 10-year age group and presence of a chronic health condition, there was no difference in the risk for ILI for those who received the vaccine, compared with those who did not (RR, 1.1; 95% CI, 0.9–1.4).

Table 3
View larger version:
Table 3

Relative Risks (RRs) and 95% Confidence Intervals (CIs) for Influenza-Like Illness (ILI) by Possible Risk Factors Recorded by the H1N1 Influenza Survey

Recent travel to Mexico was associated with ILI (RR, 2.9; 95% CI, 1.8–4.7), compared with no travel, and was reported by 22 (3%) of those with ILI. Of those patients, 20 traveled during spring break, and the median length of stay was 7 days; 7 patients had illness onset within 7 days of returning (median duration, 4 days; IQR, 1–16 days), whereas 6 became ill while in Mexico. Membership in a Panhellenic organization (RR, 2.0; 95% CI, 1.6–2.5) and participation in Greek Week activities during the period 20 April through 25 April 2009 (RR, 2.2; 95% CI, 1.8–2.8) were also associated with ILI. Nearly 10% of students reported Greek Week participation, of whom, 107 (18%) had ILI, compared with 491 (9%) with ILI among nonparticipants. Among Greek Week participants, incidence of ILI peaked during the week following the event (Figure 3).

Previous SectionNext Section

Discussion

From April through May 2009, UD experienced a dramatic increase in cases of respiratory illness and the first recognized university outbreak of pH1N1. The surge of students presenting to UDSHS with respiratory symptoms lasted ∼2 weeks and caused a substantial burden that overwhelmed the university health care system. Only 24 confirmed cases of pH1N1 infection were reported, which likely underestimates the burden of pH1N1 infection at the university. Laboratory confirmation was not routinely performed for all students who presented with respiratory illness and was discontinued when pH1N1 was confirmed on campus and the number of clinic visits increased.

Outbreaks of seasonal influenza among student and university populations have been previously reported [5, 6]. University outbreaks have resulted in increased absenteeism, impaired school performance, and increased health care utilization [7, 8]. In the context of a pandemic influenza virus, with limited knowledge about the transmission dynamics, severity of infection, effectiveness of seasonal influenza vaccine, and increased public and media attention, this large outbreak led to disruption of regular activities. Understanding the severity of pH1N1-related illness is crucial for future planning. Based on chart abstractions and an online survey, the severity of illness observed during this outbreak of pH1N1 infection in this population appeared to be consistent with seasonal influenza [5, 6, 9, 10]. Common symptoms were consistent with seasonal influenza, and very few hospitalizations and no deaths were reported among the university community, although the university represents a relatively small sample, compared with the overall population, so the range of illness, hospitalizations, and deaths could still be relatively large.

During the peak outbreak time, many individuals presented for care with nonfebrile, nonsevere illness or concern and fear of pH1N1 infection, because little was known about the illness. Furthermore, many individuals sought care because of the media attention about pH1N1. Overall, some individuals presenting to care had an acute respiratory illness that did not meet the case definition for ILI. It is unclear how many of these individuals had pH1N1 infection. To determine the extent of pH1N1 infection on campus, individuals participating in the survey and individuals whose charts were abstracted were invited to participate in a serological survey. Results of the serological survey are pending.

Future preparedness efforts for influenza outbreaks on university campuses should incorporate lessons learned from the UD outbreak, including planning for a rapid surge in the number of individuals presenting to health care facilities. Health care facilities should prepare, not only for an increase in visits for febrile illness, but also for an increase in worried persons with mild illness. In this outbreak, UD and DHSS collaborated to establish an emergency clinic to assist in evaluating students seeking care. In future outbreaks, this system could be replicated if the need for additional health services arose. Furthermore, information about illness symptoms, anticipated duration of illness, risk factors for illness, methods to prevent illness, who should seek care, when to seek care, and transmission should be provided to the community as early as possible to reduce peak burden on health care services, prevent unnecessary health care-seeking behaviors by the minimally ill, and reduce transmission. The limited adherence to guidance to reduce the risk of transmission is concerning. Development of effective communications strategies to boost compliance with nonpharmaceutical interventions will be important in preventing the spread of disease and reducing the surge in future outbreaks. In addition, CDC recommendations for higher education institutions are available online [11].

Understanding the epidemiology of ILI infection in a university outbreak not only improves our understanding of the spread of pH1N1 in this setting but may provide insights for future planning and prevention efforts in similar settings around the country and globally. ILI on the UD campus was widespread, with students being twice as likely as faculty/staff to report ILI. Students may have greater risk, because they have more close interactions with other students, although there was no difference in ILI for living on campus, compared with living off campus, and 12 individuals with confirmed pH1N1 cases lived off campus. A similar risk of infection among students who lived off campus suggests that exposure occurred in nonresidential encounters and illness spread outside the residential on-campus community in a fairly short period of time. In this population, age-specific attack rates for ILI decreased as age increased. Our results may support the finding that some older adults may be less likely to develop infection [12]. However, the decrease in attack rate with age may also be related to fewer close contacts or participation in activities that were associated with ILI among students. We found no difference in the risk of ILI for survey respondents who received seasonal influenza vaccine, compared with those who did not. Although there was limited laboratory confirmation, our investigation suggested no protective effect of the seasonal influenza vaccine against ILI or, presumably, pH1N1.

Important risk factors for ILI were travel to Mexico and participation in Greek Week activities. Recent travel to Mexico was associated with increased risk of ILI and was likely associated with introduction and early transmission of pH1N1 on campus. The greatest increase in rate of ILI was among Greek Week participants, who had twice the risk of ILI, compared with nonparticipants. The greater risk may be attributable to mixing behaviors of those who attended Greek Week relative to the rest of the student population. Based on the timeline and known influenza incubation period, it is possible that pH1N1 was introduced following spring break travel to Mexico with slow initial spread and then accelerated spread with peak in illness following Greek Week. If this is the case, it supports the concern that large social gatherings may accelerate transmission of illness in a community. Although, in this instance, Greek Week could not have been cancelled, because the outbreak had yet to be identified, the association between Greek Week and this outbreak lends some support to the idea of limiting public activities during an ongoing influenza epidemic.

In this investigation, we examined the clinical characteristics of illness, severity of illness, and effectiveness of seasonal influenza vaccine. However, this investigation had several limitations. Laboratory testing was not used on a consistent basis to confirm ILI or pH1N1 infection among all individuals with respiratory illness; rather, diagnosis was based on self-reported and clinical confirmation of symptoms. Clinical chart results may be biased by the tendency to visit the health clinic, because of the perception of widespread illness on campus. In addition, there was a 30% response rate to the survey; thus, our results may not fully represent illness on campus, although the demographic characteristics of survey participations were similar to the overall demographic characteristics of the university. Participants who responded to the survey may be different from those who did not, and individuals who experienced illness may be more likely to respond to a survey about their illness, compared with individuals who were well. Furthermore, calculations assume that all ILI was due to pH1N1, although no background rate of ILI could be calculated.

We investigated, to our knowledge, the first recognized outbreak of pH1N1 infection on a university campus. More than 10% of survey respondents reported an illness that met the case definition of ILI. Illness on campus was widespread and overwhelmed the university health system. Understanding the spread and impact of pH1N1 on a university campus is important to help prepare for future outbreaks of pandemic influenza viruses. Although the initial cases appeared to have been associated with travel to Mexico, the rapid increase in the number of reported illnesses was likely facilitated by Greek Week, which emphasizes the role of large gatherings in facilitating the transmission of influenza. Most illness was generally mild, although 4 students reported an overnight stay in the hospital, and there was no evidence that receiving a seasonal influenza vaccine prevented ILI during the study period. Given concerns about the potential scope of future pandemic influenza outbreaks, efforts may be needed to prepare for rapid increases in health care-seeking behaviors and to develop effective communication strategies that encourage behaviors to slow the spread of the virus and minimize unnecessary health care visits to reduce health care surge.

Previous SectionNext Section

acknowledgments

We thank Victor Babalban, Joan Brunkard, Kathy Byrd, Lyn Finelli, Daniel Fishbein, Mark Lamias, Harvey Lipman, Micah Milton, and Roniel T. Werman, of the Centers for Disease Control and Prevention; Deri Austin, Paula Eggers, Leroy Hathcock, Rick Hong, Ashley Love, Karyl Rattay, Sue Shore, and Crystal Webb, of the Division of Public Health, Delaware Health and Social Services; JJ Davis, Scott Douglas, Michael Gilbert, Bruce Raker, Daniel Rich, and Richard Sacher of the University of Delaware; and Sharon Bathon, Walt Dabell, Robin Elliott, Stephen P. Grasson, Albert Homiak, Marcia Nickle, Sheryl Whitlock, and the rest of the staff of Student Health Services of University of Delware.

Potential conflicts of interest. All authors: no conflicts.

  • Received September 14, 2009.
  • Accepted October 22, 2009.
Previous Section
 

references

  1. ↵
    1. Dawood FS,
    2. Jain S,
    3. et al
    Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team, Dawood FS, Jain S, et al. Emergence of a novel swine-origin influenza A (H1N1) virus in humans. N Engl J Med 2009;360:2605-15.
    CrossRefMedline
  2. ↵
    University of Delaware facts and figures 2008–2009. Available at: http://www.udel.edu/IR/fnf/index.html. Accessed 18 May 2009.
  3. ↵
    University of Delaware quick facts 2008. Available at: http://www.udel.edu/IR/facts/. Accessed 16 May 2009.
  4. ↵
    University of Delaware Student Centers. Fraternity and sorority life. Available from: http://www.udel.edu/student-centers/FandS/index.html. Accessed 16 May and 22 July 2009.
  5. ↵
    1. Pons VG,
    2. Canter J,
    3. Dolin R
    . Influenza A/USSR/77 (H1N1) on a university campus. Am J Epidemiol 1980;111:23-30.
    Abstract/FREE Full Text
  6. ↵
    1. Sobal J,
    2. Loveland FC
    . Infectious disease in a total institution: a study of the influenza epidemic of 1978 on a college campus. Public Health Rep 1982;97:66-72.
    MedlineWeb of Science
  7. ↵
    1. Nichol KL,
    2. D'Heilly S,
    3. Ehlinger E
    . Colds and influenza-like illnesses in university students: impact on health, academic and work performance, and health care use. Clin Infect Dis 2005;40:1263-70.
    Abstract/FREE Full Text
  8. ↵
    1. Nichol KL,
    2. Nordin J,
    3. Mullooly J
    . Influence of clinical outcome and outcome period definitions on estimates of absolute clinical and economic benefits of influenza vaccination in community dwelling elderly persons. Vaccine 2006;24:1562-8.
    CrossRefMedlineWeb of Science
  9. ↵
    1. Mullooly JP,
    2. Bridges CB,
    3. Thompson WW,
    4. et al
    . Influenza- and RSV-associated hospitalizations among adults. Vaccine 2007;25:846-55.
    CrossRefMedlineWeb of Science
  10. ↵
    1. Thompson WW,
    2. Comanor L,
    3. Shay DK
    . Epidemiology of seasonal influenza: use of surveillance data and statistical models to estimate the burden of disease. J Infect Dis 2006;194(Suppl 2):82-91.
    CrossRef
  11. ↵
    Centers for Disease Control and Prevention (CDC). CDC guidance for responses to influenza for institutions of higher education during the 2009–2010 academic year. Available at: http://www.cdc.gov/h1n1flu/institutions/guidance/. Accessed 29 October 2009.
  12. ↵
    Serum cross-reactive antibody response to a novel influenza A (H1N1) virus after vaccination with seasonal influenza vaccine. MMWR Morb Mortal Wkly Rep 2009;58:521-4.
    Medline
| Table of Contents

This Article

  1. Clin Infect Dis. (2009) 49 (12): 1811-1820. doi: 10.1086/649555
  1. AbstractFree
  2. » Full Text (HTML)Free
  3. Full Text (PDF)Free

Classifications

Share

  1. Email this article

Navigate This Article

Current Issue

  1. March 1, 2012 54 (5)
  1. Clinical Infectious Diseases
  1. Alert me to new issues

Most