‹ ›
Table of Contents

Effect of flu immunization programs on ED volumes

Letters

CJEM 2002;4(5):318-320

To the Editor:

The Groll and Henry article on the effect of influenza immunization programs on ED volumes is an excellent effort to identify some of the predictors of ED usage and volume,1 but several issues should be highlighted.

First, the extent of coverage of the population in question is critical to the assessment of the impact of immunization. This was pointed out by the authors in the Discussion, under "Limitations," but it cannot be overstated. If a significant proportion of the population does not receive vaccine in the first place, the program's impact will be muted or nonexistent. A Health Canada telephone survey of over 3500 individuals from across Canada during the 2000-2001 flu season showed that close to 70% of adults 65 years and older received influenza vaccine during the 2000-2001 influenza season. In contrast, only 40% of those 18 to 64 years of age with high-risk medical conditions and 55% of health care workers were immunized during that season.2 Are these immunization rates sufficient to influence ED volumes? Not likely!

In addition, if one is trying to assess the impact of a provincial influenza immunization campaign, ED volumes are only one outcome measure -- and not a sensitive one. As Groll and Henry demonstrated, influenza and pneumonia make up a small proportion of total ED visits. At St. Paul's Hospital, pneumonia, for example, accounts for about 1% of ED visits. Consequently, other factors will have a much more profound impact on ED volumes, potentially obscuring small but meaningful benefits of a vaccination program. These other factors might include the development of new ED facilities, creation of a fast-track area, changing community demographics, changing ED processes, and even ED overcrowding itself -- which has negative effects on publicity and ED volumes. The authors of this article made no attempt to compare year-by-year changes in ED volumes of influenza and pneumonia alone.

We recently measured the impact of a mass pneumococcal/influenza vaccination campaign on our ED. In November 1999 more than 8000 residents of the Downtown East Side of Vancouver were vaccinated, and we showed a 25% decrease in both ED cases of influenza and pneumonia year over year.3 The drop in pneumonia volumes was seen in both admitted and discharged patients, but was not seen in lower mainland hospitals outside the Downtown (i.e., vaccination) area.

Finally, the major reason for enhanced influenza immunization programs and, even ED immunization programs, is not to decrease ED volumes, even though this is a stated objective of the Ontario government. The influenza vaccine prevents illness in approximately 70% to 90% of healthy persons younger than age 65 years. Among elderly persons living outside nursing homes or similar chronic care facilities, influenza vaccine is 30%-70% effective in preventing hospitalization for pneumonia and influenza.4 Providing the vaccine in our EDs represents a community service and a way of decreasing morbidity and mortality in our patient population. Many of our patients, especially the disadvantaged and indigent, use our facilities as their only source of medical care. We should wholeheartedly embrace the concept of ED influenza immunization in the same way we routinely provide tetanus prophylaxis.

Eric Grafstein, MD 
St. Paul's Hospital 
Vancouver, BC

References

  1. Groll D, Henry B. Can a universal influenza immunization program reduce emergency department volume? CJEM 2002;4(4):245-51.
  2. Health Canada. Influenza [information sheet]. Nov 2001. Available: www.hc-sc.gc.ca/pphb-dgspsp/publicat/info/infflu_e.html
  3. Grafstein E, Daly P, Buxton J, Thorne A. Effect of a pneumococcal vaccine program on emergency department presentations [abstract]. CJEM 2001;3(2):143.
  4. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep 1999; 48(RR-4):1-28.

[One of the authors responds:]

I thank Dr. Grafstein for his interest in our research regarding the impact of the Ontario universal immunization program on ED volume,1 and I appreciate the opportunity to respond to some of the issues he has highlighted.

I agree with Dr. Grafstein that the issue of immunization coverage is critical when evaluating the success of an immunization program. The lack of any systematic method of collection of this data by the Ontario government prior to implementing a now $81-million program is something the Ontario taxpayers should be concerned about.

However, even on the assumption that 100% of Ontarians were immunized and all influenza eliminated in Ontario, our research1 and others2 have found that respiratory disease accounts for approximately 10% of the admissions to the ED in Ontario, and we found that over a 5-year period influenza and pneumonia combined accounted for 0.34% of visits. Based on these numbers, we concluded that even by removing all influenza cases it is hard to see how this will significantly impact overall ED volume.

As Dr. Grafstein points out, the outcome of reducing ED volume is not a sensitive measure, and there are many different and very complex issues that combine to affect ED volume. He further mentions, and I would like to stress, that this outcome was chosen by the Ontario government as 1 of only 2 reasons for implementing this program.3 I would like to add that it is not an outcome that would be chosen by most researchers examining the efficacy of such a program without sufficient empirical evidence that influenza had a major impact on ED volume. However, because it was the reason given for initiating a universal immunization campaign this is why we chose to study it.

Finally, I would like to separate the issue of the potential public health benefits of vaccination for influenza from that of ED volume. As stated by Dr. Grafstein, immunization has been shown to reduce mortality and morbidity in populations at high risk for complications from influenza,4,5 and Ontario has been providing free influenza vaccinations to this population since 1984. Although the cost and effectiveness of mass immunization programs for low-risk individuals has been questioned,6-10 targeting and enhancing the immunization rates of high-risk people may be a more cost-efficient and efficacious way to further reduce hospitalization and mortality within the population. One way to accomplish this goal may be ED immunization programs. Our study focused only on the goal of reducing ED volume and the ability of a universal influenza immunization program to achieve this end.

Dianne Groll, RN, BScH, MSc, PhD (candidate) 
ICU Research 
Kingston General Hospital 
Kingston, Ont.

References

  1. Groll D, Henry B. Can a universal influenza immunization program reduce emergency department volume? CJEM 2002;4(4):245-51.
  2. Hospital Report Research Collaborative. Hospital report 2001: emergency department care. Toronto (ON): Ont Hosp Assoc and the Govt of Ontario, editors; Dec 2001. Available: www.hospitalreport.ca/HospitalReport2001EDReport.htm (accessed 2002 Aug 22).
  3. Ontario invests $38 million to ease emergency room pressures with universal vaccination program [press release]. Toronto (ON): Govt of Ontario; 2000 July 25.
  4. Gross PA, Hermogenes AW, Sacks HS, Lau J, Levandowski RA. The efficacy of influenza vaccine in elderly persons: a meta-analysis and review of the literature. Ann intern Med. 1995;123:518-27.
  5. Govaert TM, Thijs CT, Masurel N, Sprenger MJ, Dinant GJ, Knottnerus JA. The efficacy on influenza vaccination in elderly individuals: a randomized double-blind placebo-controlled trial. JAMA 1994;272:1661-5.
  6. Monto AS. Preventing influenza in healthy adults -- the evolving story. JAMA 2000;284:1699-700.
  7. Patriarca PA, Strikas RA. Influenza vaccine for healthy adults? N Engl J Med 1995;333:933-4.
  8. Schabas RE. Mass vaccination in Ontario: a sensible move. CMAJ 2001;164(1):36-7.
  9. Demicheli V. Mass influenza vaccination in Ontario: Is it worthwhile? CMAJ 2001;164(1):38-39.
  10. Demicheli V, Jefferson T, Rivetti D, Deeks J. Prevention and early treatment of influenza in healthy adults. Vaccine 2000;18:957-1030.

To the Editor:

Groll and Henry1 are to be commended for tackling the complex and controversial issue of influenza and its relationship to ED utilization. They compared annual influenza rates across Ontario with total winter ED visits at selected EDs and found that the two were not related. They concluded that influenza does not impact ED volume and that influenza vaccination is unlikely to alleviate ED overcrowding. These conclusions have substantial public health implications. However, we are concerned that their methods may be flawed and their conclusions premature.

For each city, their analysis was based on 5 observations (i.e., 5 years). Not only was the power to detect a difference limited, but such a small number of observations may seriously compromise the stability of the statistical model used. Further, the use of such standard models to examine longitudinal data is often plagued by autocorrelation, since the data does not fulfill the assumption that observations are independent from each other (e.g., the volume of a given ED in one year is associated with its volume the next).

The outcome measure was also problematic. As the authors note, total ED volume fluctuates widely due to many factors, and ED overcrowding has not been shown to be related to ED volume in several studies.2,3 This is mainly because the majority of ED patients are young, low-acuity patients, often with minor injuries, who are unlikely to contribute substantially to overcrowding.4 Hence, the increasing overcrowding likely relates not so much to changes in total ED volume, but to an older and sicker ED patient population, more of whom may require admission than in the past.

If influenza is a contributor to this phenomenon, one would be more likely to detect the effect by focusing on older patients with complications of influenza likely requiring admission, such as pneumonia, asthma/COPD and congestive heart failure, all of which have been shown to be related to influenza outbreaks.5 The authors looked at only some of these conditions, and only for all age groups combined, and again with limited power. Other studies have found significant associations between influenza outbreaks and ED overcrowding,6 as well with increased ED utilization by the elderly.7

For all of these reasons, conclusions regarding the absence of benefit of influenza vaccination campaigns on ED utilization are likely premature and possibly incorrect. A full understanding of the impact of influenza outbreaks on EDs is still lacking.

Michael Schull, MD 
Muhammad Mamdani, PhD
Sunnybrook & Women's College Health Sciences Centre and 
Institute for Clinical Evaluative Sciences 
Toronto, Ont.

References

  1. Groll D, Henry B. Can a universal influenza immunization program reduce emergency department volume? CJEM 2002;4(4):245-51.
  2. Schull MJ, Szalai JP, Schwartz B, Redelmeier DA. Emergency department overcrowding in Toronto from 1991 to 2000: the effect of systematic hospital restructuring [abstract]. CJEM 2001;3(2):122.
  3. Morgan K, Prothero D, Frankel S. The rise in emergency admissions -- crisis or artefact? Temporal analysis of health services data. BMJ 1999;319(7203)158-9.
  4. Chan B, Schull MJ, Schultz S. Atlas of emergency department services in Ontario 1992/1993 to 1999/2000. ICES Atlas Report Series. Toronto (ON): Institute for Clinical Evaluative Sciences; 2001.
  5. Upshur RE, Goel V. Measuring the impact of influenza on the hospital admission rates of the elderly in Ontario: a five-year admission rate analysis, 1988-1993. Can J Public Health 2000;91(2):144-7.
  6. Schull MJ, Mamdani M. How influenza outbreaks affect emergency department overcrowding and ambulance diversion [abstract]. Acad Emerg Med 2001;8(5):574.
  7. Schull MJ, Mamdani M, Redelmeier DA. Influenza in elders and emergency department overcrowding [abstract]. Acad Emerg Med 2002;9(5):515.

[One of the authors responds:]

I appreciate the comments by Drs Schull and Mamdani on our study of influenza and ED volume.1 I agree with their conclusions that our study needs to be repeated with a larger number of hospitals and for a longer time period, and hope that this will be accomplished in the near future. I also feel that a full understanding of the impact influenza on ED volume is lacking. However, I feel that this research should have been undertaken prior to the launching of the universal influenza immunization campaign.

I stress "universal immunization," because, as Drs. Schull and Mamdani point out, "the majority of ED patients are young, low-acuity patients, often with minor injuries, who are unlikely to contribute substantially to overcrowding. Hence, the increasing overcrowding likely relates ... to an older and sicker ED patient population, more of whom may require admission than in the past."2,3 However, the older, high-risk patients were not the primary target of the universal immunization campaign, and they have been provided free influenza vaccinations since the 1980s.1 If one concludes that the high-risk population is responsible for ED overcrowding then concentrating efforts on increasing their immunization compliance may be a more effective strategy. None of the above information changes the fact that ED volume is highest in the summer, when there are few influenza cases.1,3

Finally, Drs. Schull and Mamdani state that "other studies have found significant associations between influenza outbreaks and ED overcrowding,4...". Unfortunately, the outcome of ambulance diversion as a measure of ED overcrowding is not universal nor uniform, as many hospitals are simply not able to divert ambulances. Furthermore, ambulance diversion is an administrative decision and can be based on several criteria such as beds available outside the ED and ED staffing, and these may vary at different hospitals. Using ambulance diversion as the outcome in Kingston, for example, would result in no relationship between ED volume and diversion, because Kingston is not able to divert ambulances.

Once again, I thank Drs. Schull and Mamdani for their interest in this research and look forward to more studies on the impact of influenza immunization on ED volume.

Dianne Groll, RN, BScH, MSc, PhD (candidate) 
ICU Research 
Kingston General Hospital 
Kingston, Ont.

References

  1. Groll D, Henry B. Can a universal influenza immunization program reduce emergency department volume? CJEM 2002;4(4):245-51.
  2. Schull MJ, Mamdani M, Redelmeier DA. Influenza in elders and emergency department overcrowding [abstract]. Acad Emerg Med 2002;9(5):515.
  3. Chan B, Schull MJ, Schultz S. Atlas of emergency department services in Ontario 1992/1993 to 1999/2000. ICES Atlas Report Series. Toronto (ON): Institute for Clinical Evaluative Sciences; 2001.
  4. Schull MJ, Mamdani M. How influenza outbreaks affect emergency department overcrowding and ambulance diversion [abstract]. Acad Emerg Med 2001;8(5):574.
‹ ›
Table of Contents