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© 2004 American Public Health Association
RESEARCH AND PRACTICE |
At the time of the study, all the authors were with the Michigan Department of Community Health, Lansing, Mich. Revathi R. Ramani and Matthew Boulton also were with the University of Michigan Preventive Medicine Residency Program, Ann Arbor.
Correspondence: Requests for reprints should be sent to William N. Hall, Bureau of Epidemiology, Mich Dept of Community Health, 3423 N Martin Luther King Blvd, Lansing, MI 48909 (e-mail: hallw{at}michigan.gov).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONReferences |
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We examined the impact of the heptavalent pneumococcal conjugate vaccine (PCV7) on hospital discharge rates for invasive pneumococcal disease among Michigan children younger than 5 years old. After the introduction of PCV7, the hospital discharge rate for children younger than 1 years old was significantly lower than before introduction. We correlated the decreased rates with the introduction and rapid uptake of PCV7. Lack of change in the hospital discharge rates for other age groups likely represents a slower uptake of PCV7 compared with that for children aged younger than 1 year.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONReferences |
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Before the heptavalent pneumococcal conjugate vaccine (PCV7) was introduced, Streptococcus pneumoniae (pneumococcus) caused approximately 17 000 cases of invasive disease annually among US children aged younger than 5 years.1 PCV7 was licensed in February 2000 and is recommended for universal use among children aged 2 to 23 months.1,2 Of the more than 90 serotypes of pneumococcus, PCV7 protects against the 7 most common serotypes that comprise 80% of all invasive pneumococcal diseases among children aged younger than 6 years.1,3 PCV7 decreased invasive infections by more than 93% during efficacy trials.4,5
A previous study that examined data from the Active Bacterial Core Surveillance showed a decrease in the invasive disease rate among children aged 2 years and younger.6 Our ecological study analyzed whether Michigan’s hospital discharge rates for invasive pneumococcal disease decreased among children younger than 5 years after the introduction of PCV7.
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONReferences |
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We identified invasive pneumococcal disease cases by hospital discharge diagnostic codes (International Classification of Diseases, 9th Revision [ICD-9])7 through the Michigan Inpatient Database. We defined invasive pneumococcal disease cases as any discharge that met the case definition for either pneumococcal meningitis (ICD-9 codes 320.1 or 320.8 and 041.2) or pneumococcal bacteremia (ICD-9 codes 038.2 or 790.7 and 041.2 or 038.9 and 041.2).
We used the Michigan Inpatient Database and the annual intercensal population estimates from Michigan’s Office of the State Demographer to calculate discharge rates per 100 000 patients from July 1994 through June 2001. We categorized age groups in accordance with the Active Bacterial Core Surveillance of the Emerging Infections Program Network: less than 1 year, 1 year, and 2 through 4 years.8
We reviewed data from the Michigan Childhood Immunization Registry to assess PCV7 uptake. As of August 2001, 71% of all vaccine providers in Michigan were enrolled in the Michigan Childhood Immunization Registry.9 We used SAS software (SAS Institute Inc, Cary, NC) to compare discharge rates before (July 1994 to June 2000) and after (July 2000 to June 2001) the introduction of PCV7. We also used logistic regression to evaluate whether the discharge rates after introduction of the vaccine deviated from the trends before introduction.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONReferences |
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From January 2000 to June 2001, more than half of the doses of PCV7 were given to children younger than 1 year, and about one quarter of the doses were given to children aged 12 to 23 months. Almost 50% of children aged 7 months who were registered in the Michigan Childhood Immunization Registry had received 3 doses of PCV7 by June 2001.
For children younger than 1 year, the average annual hospital discharge rate for pneumococcal bacteremia before the introduction of PCV7 was 26.4, which was significantly higher than the rate after introduction (14.9; P = .013). Similarly, the average annual discharge rate for invasive disease before the introduction of PCV7 (40.0) also was significantly higher than the rate after introduction (23.9; P = .0049) (Figure 1
). Logistic regression analyses showed that the discharge rates of both pneumococcal bacteremia and invasive disease after the introduction of PCV7 deviated from the general trends before introduction; however, the 95% confidence intervals for the predicted and the observed rates overlapped slightly. Conversely, the average annual hospital discharge rate for pneumococcal meningitis before the introduction of PCV7 (13.6) was not significantly different after introduction (9.0; P = .168). All other age groups did not show a significant change in discharge rates for invasive pneumococcal illness after the introduction of PCV7.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONReferences |
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We correlated the significant decrease in the hospital discharge rates for invasive disease among children younger than 1 year with increased vaccine uptake. The only major change in medical practice regarding invasive pneumococcal disease from July 1999 through June 2000 was the introduction of PCV7, which makes it the most plausible explanation for the decline in hospital discharge rates. We did not observe a similar decline in older age groups, probably because the majority of doses were given to children aged younger than 1 year.
The small number of pneumococcal meningitis cases hindered trend analysis. Although we did see a decline in hospital discharge rates in June 2001, it was not statistically significant. It may be too early after the introduction of PCV7 to see the full decrease that might occur for incidences of pneumococcal meningitis.
Our study has several limitations. First, we used the Michigan Inpatient Database as the source of data, and we defined pneumococcal diseases solely by ICD-9 codes, which may have led to miscoding because a nosologist is not directly involved in the patient’s care. Second, this was an ecological study and the results may be biased. We were unable to correlate the vaccination status directly with the occurrence of pneumococcal disease at the individual patient level. Third, the short study period of sustained vaccine uptake after the introduction of PCV7 hindered the analysis of secular trends in the hospital discharge rates. The goal of our study, however, was to provide a rapid assessment of invasive disease rates after the introduction of PCV7.
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CONCLUSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONReferences |
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Preliminary evidence shows that in the short study period, the use of PCV7 is correlated with decreased hospital discharge rates for invasive pneumococcal disease.
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Acknowledgments |
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The authors gratefully acknowledge Joanne Hogan, PhD, and Thu Le, PhD, for their help in accessing the Michigan Inpatient Database and obtaining intercensal information. The authors also acknowledge Robert Swanson, MPH, and Kyle Enger, MPH, for accessing the Michigan Childhood Immunization Registry.
Human Participant Protection
No protocol approval was needed for this study.
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Footnotes |
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Contributors
R. Ramani led topic selection, data collection, analysis, and writing; the other authors assisted.
Accepted for publication July 26, 2003.
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References |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONReferences |
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1. Centers for Disease Control and Prevention. Preventing pneumococcal disease among infants and young children: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep.2000;49:1–35.[Medline]
2. Anonymous. American Academy of Pediatrics. Committee on Infectious Diseases. Policy statement: recommendations for the prevention of pneumococcal infections, including the use of pneumococcal conjugate vaccine (Prevnar), pneumococcal polysaccharide vaccine, and antibiotic prophylaxis. Pediatrics.2000;106(2 Pt 1):362–366.
3. Robinson KA, Baughman W, Rothrock G, et al. Epidemiology of invasive Streptococcus pneumoniae infections in the United States, 1995–1998: opportunities for prevention in the conjugate vaccine era. JAMA.2001;285(13):1729–1735.
4. Lieu TA, Ray GT, Black SB, et al. Projected cost-effectiveness of pneumococcal conjugate vaccination of healthy infants and young children. JAMA. 2000;283(11):1460–1468.
5. Overturf GD. American Academy of Pediatrics. Committee on Infectious Disease. Technical report: prevention of pneumococcal infections, including the use of pneumococcal conjugate and polysaccharide vaccines and antibiotic prophylaxis. Pediatrics. 2000;106(2 Pt 1):367–376.
6. Whitney CG, Farley MM, Hadler J, et al. Decline in invasive pneumococcal disease after the introduction of protein-polysaccharide conjugate vaccine. New Engl J Med.2003;348(18):1737–1746.
7. International Classification of Diseases, 9th Revision. Geneva, Switzerland: World Health Organization; 1980.
8. Centers for Disease Control and Prevention, Division of Bacterial and Mycotic Diseases. Streptococcus pneumoniae Disease Technical Information. 2001. Available at http://www.cdc.gov/ncidod/dbmd/diseaseinfo/streppneum_t.htm. Accessed May 13, 2002.
9. Michigan Public Health Institute. Michigan Childhood Immunization Registry. 2001. Available at http://www.mcir.org. Accessed October 21, 2002.
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