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Hawaii Med J. Jun 2010; 69(6 Suppl 3): 50–51.
PMCID: PMC3123141

Guam's Influenza Epidemic(s) of 2009

Abstract

Objective

To characterize syndromic and laboratory surveillance for influenza on Guam during 2009, including the relation of cases to the timing of swine flu-related stories published in a local newspaper.

Methods

Data utilized in the study included clinical diagnoses of acute respiratory infection (ARI) in the Emergency Department log of Guam's only civilian hospital (syndromic surveillance) and laboratory confirmed cases of Influenza A (rapid test) and novel 2009 H1N1 influenza virus (RT-PCR subtyping) from both civilian and military sources. In addition, the number of “swine flu” stories appearing weekly in a local paper were tallied.

Results

What initially appeared to be an epidemic occurring in 2 distinct waves was shown to be separate epidemics of “seasonal flu” and “swine flu.” There was a strong correlation between the timing of “swine flu”stories appearing in local media and the diagnosis of ARI.

Conclusion

Syndromic surveillance is useful for the early detection of disease outbreaks but laboratory results may be necessary in order to gain a clear epidemiologic picture of a disease incident.

Introduction

In 1974 the investigation of an unusual food poisoning incident on Guam led to the discovery of the first case of cholera to be identified in Micronesia.1 Since it was suspected that additional unidentified cases of cholera might be occurring on the island, a program of syndromic disease surveillance (monitoring groups of signs and symptoms rather than only laboratory-confirmed disease) was initiated to detect possible otherwise unobserved disease trends. Since then daily entries in the Guam Memorial Hospital Authority (GMHA-Guam's sole civilian hospital) Emergency Department patient log have been reviewed and clinical diagnoses tallied. In addition to monitoring the levels of diarrheal disease diagnosed, the numbers of acute respiratory infections (ARI - including flu, flu syndrome, pharyngitis, URI, bronchitis, pneumonia, etc.), chronic respiratory disease (asthma, chronic obstructive pulmonary disease), rash illnesses accompanied by fever, influenza or influenza-like-illnesses, conjunctivitis, total patients seen and total patients admitted to hospital are also collected.2

An early evaluation of 2009 syndromic acute respiratory infection diagnoses (ARI diagnoses through week 41) treated in the Guam Memorial Hospital Emergency Department (GMH-ED) demonstrated two peaks in 2009. It was hypothesized that these peaks may have reflected successive waves of 2009 H1N1 influenza (Figure 1).3 As additional data for all of 2009 became available this conclusion was reexamined.

Figure 1
Cases of syndromic ARI seen in the GMH-ER during the first 41 weeks in 2009.

Methods

To examine the hypothesis that the 2009 H1N1 epidemic on Guam had occurred in 2 waves, 4 sets of disease data for calendar year 2009 were collected and compared. In addition to syndromic ARI cases, these data sets included island-wide (including military, public health and private clinics) laboratory-confirmed H1N1 cases and cases of rapid-test positive influenza A that were negative for H1N1 (Figure 2). Patient specimens positive for influenza A by rapid test were submitted either to the WHO Collaborating Laboratory in Melbourne, Australia (civilian specimens) or the US Naval Research Center, San Diego, California (military specimens). Because it was suspected that news stories appearing in local media about swine flu cases, first in Mexico and later in the US and world-wide, may have influenced people to seek medical attention, an analysis of news stories appearing in Guam's major newspaper (Pacific Daily News) was undertaken. By visiting the paper's web page (www.guampdn.com) and using the search engine provided, it was possible to tally the number of news stories about swine flu that appeared in the paper each week during 2009 and compare these figures with the number of ARI cases recorded (Figure 3). Statistical analysis software (SAS®) Institute Inc., Version 9, Cary, North Carolina, 2008) was used to calculate a Pearson's correlation coefficient to quantify the linear relationship between the number of news stories and the number of ARI diagnoses.

Figure 2
Comparison of confirmed H1N1 and “other” influenza A cases, Guam, 2009.
Figure 3
Comparison of number of published “swine flu” news articles and hospital Emergency Room ARI data by week, Guam, 2009.

Results

Syndromic surveillance data of ARI collected from the GMHA Emergency Department log during 2009 suggested that there may have been 2 “waves” of the 2009 swine flu epidemic on Guam, the first beginning in early May (week 18) and lasting for 6 weeks and a second larger wave beginning in late June (week 26) and lasting for 18 weeks [Fig. 1]. However, when the final count for the year of laboratory-confirmed influenza cases reported to Guam Public Health by both civilian and military health providers was available it became clear that it was influenza A viruses other than H1N1 that had occurred in 2 waves and that Guam's H1N1 cases had occurred in a single rather sharply demarcated wave beginning during the 23rd week (week ending June 13, 2009) and disappearing during week 37 (week ending September 19, 2009 )[Fig, 2].

Analysis of news stories appearing in Guam's major newspaper (Pacific Daily News) revealed a striking positive correlation between the timing of swine flu articles and the number of patients seen in the ER and diagnosed with ARI [Fig. 3] (Pearson correlation coefficient = 0.647, P < 0.05) with each of the two major peaks in the number of ARI illnesses being preceded by a peak in swine flu news stories.

Discussion

Along with most other areas of the world, Guam experienced an epidemic of Pandemic (H1N1) influenza virus (commonly, if inappropriately, referred to as swine flu) during 2009. This particular flu virus proved to not be particularly pathogenic; a total of 337 cases of laboratory-confirmed H1N1 and 2 deaths were reported to Guam Public Health for a case mortality rate of 0.6% (the U.S. rate may have been approximately 2.7%4). In contrast, worldwide there were 72 cases and 32 deaths of H5N1 (avian flu) in 2009 giving a case mortality rate of 44.4%. Fortunately the avian flu virus has so far not developed the ability to spread efficiently from person to person so its capacity to cause widespread epidemics in the human population has been limited.

There could be several explanations for the correlation observed between local news stories and the incidence of acute respiratory disease seen in the local Emergency Department. First off, discarding the possibility that the flu virus was being spread by the local newspaper (as such a scenario is not consistent with current knowledge about the epidemiology of the H1N1 flu virus which has shown that it was spread efficiently from person to person5,6) what seems plausible is that as people read stories about the spread of swine flu in Mexico and the United States they became increasingly concerned about their own health and were more likely to seek medical intervention if they developed flu-like symptoms. In addition, once physicians were alerted to the fact that a novel influenza virus was rapidly spreading throughout the world, they may have been more likely to consider influenza as an appropriate diagnosis and to report suspect cases to public health authorities.

Although this study demonstrated the utility of syndromic surveillance in rapidly identifying a disease outbreak, there were also some limitations. One was lack of inclusion of syndromic ARI data from the US Naval Hospital Guam and public or private medical clinics other than the GMH-ED. Inclusion of this information would have increased the total number of clinical diagnoses and would have changed the Pearson correlation coefficient. A second limitation was potential differences in clinical diagnoses by individual attending physicians in the GMH-ED. This may have resulted in missed cases, both clinical and laboratory confirmed. Other factors such as the demographics of those who read the newspaper and those diagnosed with ARI or influenza were not available for analysis. These measures could have helped further clarify the association between the published swine flu articles and the clinical diagnoses of ARI.

Footnotes

No funding or fees were received specifically for this project.

References

1. Haddock RL. Cholera in a Pacific Island. J Diarrhoeal Dis Res. 1987;5(3):181–183. [PubMed]
2. Haddock RL. Disease Surveillance in Guam: a historical perspective. Pac Health Dialog. 2005 Sep;12(2):121–126. [PubMed]
3. Haddock RL, Mathew A. Influenza HINI on Guam. Inform'ACTION No. 31. Noumea: Secretatiat of the Pacific Community; 2009.
4. Reed C, Angulo FJ, Swerdlow DL, Lipsitch M, Meltzer MI, Jernigan D, Finelli L. Estimates of the prevalence of pandemic (H1N1) 2009, United States, April–July 2009. Emerg Infect Dis. 2009 Dec;15(12):2004–2007. [PMC free article] [PubMed]
5. Centers for Disease Control and Prevention (CDC), author Outbreak of 2009 pandemic influenza A (H1N1) at a school - Hawaii, May 2009. MMWR Morb Mortal Wkly Rep. 2010 Jan 8;58(51):1440–1444. [PubMed]
6. Cauchemez S, Donnelly CA, Reed C, Ghani AC, Fraser C, Kent CK, Finelli L, Ferguson NM. Household transmission of 2009 pandemic influenza A (H1N1) virus in the United States. N Engl J Med. 2009 Dec 31;361(27):2619–2627. [PMC free article] [PubMed]

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