Polio Eradication: Surveillance Implications for the United Kingdom. D. M. Salisbury, M. E. Ramsay, J. M. White, and D. W. Brown. Department ofHealth ...
S156
Polio Eradication: Surveillance Implications for the United Kingdom D. M. Salisbury, M. E. Ramsay, J. M. White, and D. W. Brown
Department of Health, Communicable Disease Surveillance Centre, Virus Reference Division, Public Health Laboratory Service, London, United Kingdom
The requirements for certification of elimination of wild virus poliomyelitis will pose particular problems for some industrialized countries, such as the United Kingdom, where there has been no case detected for at least a decade. Systems of surveillance of poliomyelitis have been reviewed and potential weaknesses identified. When oral polio vaccine is routinely used, the rate of vaccineassociated cases provides an indication of the likelihood that if they occurred, wild virus cases would be detected. Acute flaccid paralysis surveillance was done for 3 years, but rates were lower than reported elsewhere and were accepted for certification purposes. Alternative techniques, such as surveillance of polioviruses, either in clinical samples or from the environment, may be developed in such countries. The ability to identify enteroviruses and to distinguish between wild and vaccine strains of polioviruses will give assurance that silent transmission of wild viruses is unlikely.
The opinions expressed herein are those of the authors, rather than the Department of Health and the Public Health Laboratory Service. Reprints or correspondence: Dr. D. M. Salisbury, Department of Health, 707 Wellington House, 133-155 Waterloo Rd., London SE1 8UG, UK. The Journal of Infectious Diseases 1997; 175(8uppl 1):8156-9 © 1997 by The University of Chicago. All rights reserved. 0022-1899/97/7581-0027$01.00
At the same time that augmented immunization activities were being implemented, new surveillance systems were being developed. In order to have the highest probability of detecting any cases of poliomyelitis, all cases of acute flaccid paralysis (AFP) in children < 15 years old (later reduced to children 25,000 stool samples from paralyzed persons and their childhood contacts were examined in the Americas, and no wild polioviruses were detected. It would be expected that if wild poliovirus was in circulation, such samples would detect the viruses. Currently, laboratories in England and Wales report all confirmed poliovirus isolates to the PHLS CDSC. Most viruses are isolated in the stools of young children with gastroenteritis who have samples taken shortly after vaccination with oral polio vaccine. During 1993-1994, as part of a pilot scheme to enhance surveillance, isolates from several laboratories were submitted to the PHLS Enteric and Respiratory Virus Laboratory to be characterized as Sabin-like or wild strains by immunologic and molecular tests. During 1994, 200 poliovirus strains were received: 70 type 1, 63 type 2, and 67 type 3. All 183 isolates thus far characterized have proved to be Sabin vaccine-like strains. To ensure that imported strains of wild poliovirus are not circulating in the community, it is now proposed to extend this surveillance to all poliovirus strains isolated in England and Wales. Because it is known that most poliovirus infection is subclinical, it has been suggested that the detection and characterization of polioviruses in the environment would provide useful surveillance data. Routine environmental surveillance for poliovirus through sewage monitoring is unlikely to be practical
Downloaded from jid.oxfordjournals.org at The Reference Shelf on July 14, 2011
Over the 3 years, 120 children were reported through the scheme. The overall rate of reports has been 0.38/100,000 children < 16 years old/year. The rate was 0.48/100,000 during the first year of the scheme, 0.34 during the second year, and 0.34 during the third year, suggesting that reporting rates declined after the start of the surveillance (figure 2). Overall, 54% of cases were known to have had at least 1 stool specimen taken for virology; 15% had 2 stool samples sent. There did not appear to be any identifiable trends in compliance for collection of stool samples during the surveillance period. Sixty-nine (58%) of 120 AFP cases were diagnosed as Guillain-Barre syndrome. In 11 cases (9.1%), no diagnosis has yet been allocated, although follow-up of outstanding reports continues (table 2). Evidence of acute infection was found in several cases of Guillain-Barre syndrome, including 2 boys (3 and 6 years) with adenovirus infection, a 2-year-old boy with reovirus infection, a l2-year-old girl with nonpolio enterovirus infection, 2 with Mycoplasma infection, 2 with Campylobacter infection, 1 each with respiratory syncytial virus, cytomegalovirus, Epstein-Barr virus, influenza virus, and adenovirus infections, and 1 who was Paul-Bunnell test-positive. Other cases of AFP, not classified as Guillain-Barre syndrome, were reported to have been caused by Coxsackie B virus (2), Mycoplasma species (2), glandular fever, and rubella vaccine (lgG- and IgM-positive with immunization 16 days previously). There were 3 polio vaccine-associated/recipient cases (type 2 in a boy at 2 months, type 1 in a boy at 3 months and another at 6 months). All of these cases were also notified to ONS. The rate of reporting of AFP in the UK study was lower than that from any country in the Americas undertaking such surveillance [6]. The low UK AFP rates, along with the progressive decline of reporting through the study period, suggest that there has been considerable failure of reporting. However,
J10 1997; 175 (Suppl 1)
JID 1997; 175 (Suppl 1)
Polio Eradication: Surveillance Implications
Conclusions The UK, along with many other European countries, has reported an absence of poliomyelitis for a decade or even longer. Computer simulations of poliovirus transmission [11] in developing countries suggest that even after 5 years without paralytic cases, the probability of silent transmission can still be in the range of 0.1%-1.0%. After a decade without paralytic cases, the UK is even more likely to be free of transmission. Because routine surveillance has not detected any cases of paralysis, this evidence would not prove the absence of circulation of wild polioviruses. From all sources, the rate of detection of vaccine-associated cases is as high as reported from other similar countries. Independent indicators of surveillance (such as AFP) are unlikely to reach the quality demonstrated in the Region of the Americas, where many countries had polio cases
until relatively recently. The standards for surveillance applied to industrialized countries, however, will need to be as rigorous as those met by less developed countries. In the UK, several new surveillance initiatives are proposed to demonstrate the absence of wild polioviruses that may be sufficient to satisfy certification procedures. Every country will gain considerably from the ability to abandon polio immunization. Countries will not benefit until there is convincing evidence worldwide that no wild polioviruses are in circulation, and the standards of evidence needed will be rigorous. The UK will need to rise to this challenge. References 1. Nathanson N, Martin JR. The epidemiology of poliomyelitis: enigmas surrounding its appearance, periodicity, and disappearance. Am J Epidemiol 1979; 110:672-92. 2. Melnick JL, Ledinko N. Social serology: antibody levels in a normal young population during an epidemic of poliomyelitis. Am J Hyg 1951; 54:354-82. 3. Chief Medical Officer/Chief Nursing Officer Letter. Vaccination against smallpox. London: Department of Health, 1980; publication nos. CMO(80)12, CNO(80)8. 4. De Quadros CA, Andrus JA, Olive lM, et al. Eradication of poliomyelitis: progress in the Americas. Pediatr Infect Dis J 1991; 10:222-9. 5. De Quadros CA, Henderson DA. Disease eradication and control in the Americas. Biologicals 1993;21:335-43. 6. Pan American Health Organization. Final report of the third meeting of the International Commission for the Certification of Poliomyelitis Eradication in the Americas. Washington, DC: PARO, 1994. 7. Joce R, Wood D, Brown D, Begg NT. Paralytic poliomyelitis in England and Wales, 1985-91. BMJ 1992;305:79-82. 8. Esteves K. Safety of oral poliomyelitis vaccine: results of a WHO enquiry. Bull WHO 1988; 66:739-46. 9. Strebel PM, Sutter RW, Cochi SL, et al. Epidemiology of poliomyelitis in the United States one decade after the last reported case of indigenous wild virus-associated disease. Clin Infect Dis 1992; 14:568-79. 10. British Paediatric Surveillance Unit. 8th annual report. London, UK: British Paediatric Association, 1993. 11. Eichner M, Dietz K. Eradication of poliomyelitis: when can one be sure that polio virus transmission has been terminated? Am J Epidemiol 1996; 143:816-22.
Downloaded from jid.oxfordjournals.org at The Reference Shelf on July 14, 2011
or scientifically meaningful in the UK, in contrast to countries with less centralized sewage systems. Two programs are planned, however, that will give information about the origin of any polioviruses circulating in the environment. To assess the threat to public health posed by possible importation, a protocol is being developed to investigate all contacts of suspected importation and to use environmental monitoring to establish the scale of transmission that takes place following an imported case. To complement this, it is planned that a representative sample of the enteroviruses already being detected as part of the statutory drinking and seawater bathing water testing will be further characterized to try to identify the presence or absence of any wild polioviruses. A small proportion of poliovirus infections are associated with aseptic meningitis. It is planned to investigate cases of aseptic meningitis by testing cerebrospinal fluid and fecal samples with a sensitive nested polymerase chain reaction with poliovirus. Using this approach in a number of sentinellaboratories should provide additional information on the presence or absence of circulation of wild poliovirus in the UK.
Sl59
