Virologic Surveillance and Progress Toward Poliomyelitis Eradication -- Eastern Mediterranean Region, 1995-September 1998

In 1988, the Regional Committee of the Eastern Mediterranean Region (EMR) * of the World Health Organization (WHO) resolved to eliminate poliomyelitis by 2000. Substantial progress toward polio eradication has been achieved in the region (1). Surveillance for cases of acute flaccid paralysis (AFP) and examination of stool specimens from AFP cases for the presence of poliovirus provide critical data to target supplemental vaccination activities. This report summarizes the progress in AFP and poliovirus surveillance in EMR from 1995 through September 1998 and highlights the importance of virologic investigations to determine whether viruses isolated represent indigenous transmission, importations, or laboratory contamination.

Laboratory Network

WHO has established a global laboratory network to support national polio eradication programs (2). Twelve laboratories constitute the regional network in EMR. National poliovirus laboratories (NPLs) in Iran, Iraq, Jordan, Morocco, Oman, Saudi Arabia, Sudan, and Syria process stool specimens from AFP cases to isolate and serotype poliovirus. Regional reference laboratories in Egypt, Kuwait, Pakistan, and Tunisia confirm the serotype of poliovirus isolated by NPLs and determine whether viruses are wild or vaccine-derived. Laboratory performance is monitored through programs of annual accreditation and proficiency testing. Nine of 12 network laboratories are accredited by WHO, and one laboratory was accredited provisionally pending improvement in timeliness of reporting; results from two nonaccredited laboratories are cross-checked by other accredited network laboratories. Ten network laboratories attained scores of greater than or equal to 80% in the most recent proficiency test, and staff of the two laboratories that performed poorly have been retrained.

Circulation of Poliovirus

Approximately 3000 AFP cases were reported in EMR in 1997. From 1995 through June 1998, the nonpolio AFP rate has increased from 0.5 to 0.8 (per 100,000 children aged less than 15 years). At least one stool specimen has been collected from greater than 80% of reported AFP cases, and "adequate stool specimens" (i.e., two stool samples collected at least 24 hours apart and within 14 days of paralysis onset) have been collected from 50% to 70% of all AFP cases reported (Table_1) since 1995. During this period no wild polioviruses were detected in Bahrain, Djibouti, Jordan, Kuwait, Lebanon, Libya, Morocco, Oman, Palestine, Qatar, Somalia, Tunisia, United Arab Emirates, and Yemen. In some countries, these negative findings may indicate the "true" absence of wild poliovirus circulation, but in other countries (e.g., Djibouti, Libya, Qatar, Somalia, United Arab Emirates, and Yemen) surveillance is either in early stages of implementation or inadequate to rule out continuing virus transmission.

Poliovirus type 1 remains endemic in Pakistan, Afghanistan, and Sudan, is contained to foci in Egypt and Iran, and has been isolated from a single AFP case in Syria with paralysis onset in March 1998. In 1997, poliovirus type 1 was isolated from two cases of AFP in Iraq, and through September 1998 wild poliovirus has not been isolated in the country. Poliovirus type 2 has not been isolated in the region during 1998, but was last isolated in Pakistan and Afghanistan in 1997. Poliovirus type 3 remains endemic in Pakistan and Afghanistan, and was isolated from one AFP case and a contact of another case in Iran and one case in Saudi Arabia in 1998. Although poliovirus type 3 was isolated in Iran in 1997, this serotype had been absent from Saudi Arabia since 1995. Epidemiologic and genomic sequencing data support transmission links of the 1998 Saudi Arabia case with Afghanistan and Pakistan. Poliovirus type 3 appears to have been eliminated from Egypt in 1996.

Genetic Characterization of Wild Poliovirus

Analysis of genetic sequences of selected poliovirus isolates has been conducted in specialized laboratories within the WHO global poliovirus laboratory network. These studies demonstrated a reduction in the number of circulating poliovirus genotypes and a reduced genetic sequence diversity among Pakistan and Egyptian poliovirus isolates. One poliovirus type 1 genotype circulated in Egypt from 1995 to 1998 during which sequence analysis of this genotype indicated a greater than 80% reduction in the independent chains of transmission. Poliovirus type 3 from Egypt isolated from 1995 to 1996 belong to a single genotype, which appears to have been eliminated. Poliovirus type 1 isolates obtained in Pakistan during 1995-1997 belong to a single genotype, in contrast to those isolated from 1990 through 1992 when four different genotypes were detected (3).

Genetic studies have provided evidence of poliovirus transmission links among certain countries. Poliovirus type 1 isolates from the Iran (1997) and Pakistan (1995 to 1997) belonged to the same genotype and had greater than 97% genetic sequence similarity. During 1997-September 1998, 17 wild poliovirus-associated cases were reported from Iran, 15 of which occurred in southeastern provinces; most had epidemiologic links to neighboring Pakistan or Afghanistan. To reduce the risk for importation of wild viruses from Pakistan and Afghanistan, joint cross-border polio vaccination activities were conducted in Iran, Pakistan, and Afghanistan in 1998 and will be repeated in 1999 and 2000.

In 1997, poliovirus transmission occurred in border areas of Turkey and Iraq, apparently facilitated by population movement and low oral poliovirus vaccine coverage. Six virologically confirmed poliovirus type 1 cases were detected in Turkey; all were in persons from Mardin province in the southeastern part of the country. In the same year, poliovirus type 1 was isolated from two of 28 persons reported with polio from Iraq: one was from Wasit province in the south and the other from Ninevah, a northern province near the southern border province of Mardin in Turkey. The 1997 poliovirus type 1 isolates from Turkey and Iraq belonged to the same genotype and genetic cluster and were closely related to 1994 Turkish isolates.

Epidemiologic and/or genetic sequence data showed that imported viruses contributed to previous polio outbreaks in some countries (e.g., Saudi Arabia, Jordan, and Oman) (4-6). The risk for wild poliovirus importation remains high in countries that have common borders or receive visitors (e.g., as tourists, refugees, pilgrims, or migrant workers) from countries where polio is endemic.

Genetic sequence analyses also were used to confirm that wild poliovirus laboratory contaminants were reported inadvertently in three different laboratories during 1995-1998. Eradication programs had been alerted to the possibility of contamination through unusual clusters of wild viruses from AFP cases without residual paralysis.

Reported by: Expanded Program on Immunization, Eastern Mediterranean Region, World Health Organization, Alexandria, Egypt. Global Program for Vaccines and Immunization, World Health Organization, Geneva, Switzerland. Respiratory and Enteric Virus Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Vaccine Preventable Disease Eradication Div, National Immunization Program, CDC.

Editorial Note

Editorial Note: Virologic surveillance for polioviruses and genetic studies of poliovirus isolates provided critical data for programmatic action. These methods allow the attribution of individual isolates of poliovirus to either indigenous transmission (i.e., poliovirus reservoir), importation, or laboratory contamination, each of which require different interventions. The highest priority must be directed toward the identification of foci of poliovirus transmission (e.g., reservoirs of continuing circulation during low season) and targeting these areas for intense repeated vaccination campaigns to eliminate the last chains of transmission.

Genetic sequence information from Pakistan isolates has been a useful program monitoring tool. Improvement in surveillance resulted in an increase in the number of reported polio cases in 1997 compared with 1996, despite implementation of recommended polio eradication strategies. Molecular studies from poliovirus isolates, however, suggested a substantial decrease in biodiversity, with many lineages of poliovirus being eliminated successively. These molecular studies emphasize the need for coordinated efforts to eliminate the remaining poliovirus reservoirs in the Iraq/Turkey border area and in Pakistan, Afghanistan, and border areas of Iran. Genomic studies for investigation of suspected laboratory contamination also can avoid the implementation of costly vaccination campaigns planned in response to the reporting of wild viruses.

Several important factors delay progress toward the eradication target. Underestimation of the geographic spread of poliovirus may occur because of inadequate AFP surveillance in some countries affected by war, civil unrest, or weak health-care systems (e.g., Somalia, Djibouti, and Yemen). Polioviruses reported in Afghanistan were detected only after AFP surveillance was implemented in 1997. Inappropriate timing, collection, and/or transport of stool specimens also decrease the sensitivity of virus isolation (7).

Virologic data indicate that substantial progress has been made toward polio eradication in the region. Continued international support ** will be essential, especially in those countries where polio is endemic and human and financial resources are limited, to continue to improve field and laboratory surveillance for poliomyelitis. Further enhancement of these systems will be needed to ensure eradication of polio by 2000.

References

1. CDC. Progress toward poliomyelitis eradication -- Eastern Mediterranean Region, 1996-1997. MMWR 1997;46:793-7.

2. CDC. Status of the global laboratory network for poliomyelitis eradication, 1994-1996. MMWR 1997;30:692-3.

3. Mulders MN, Lipskaya GY, van der Avoort HGAM, et al. Molecular epidemiology of wild poliovirus type 1 in Europe, the Middle East, and the Indian Subcontinent. J Infect Dis 1995;171:1399-405.

4. Afif H, Sutter RW, Kew OM, et al. Outbreak of poliomyelitis in Gizan, Saudi Arabia: cocirculation of wild polioviruses from three separate origins. J Infect Dis 1997;175(suppl 1):S71-S75.

5. Sutter RW, Patriarca PA, Brogan S, et al. Outbreak of paralytic poliomyelitis in Oman: evidence of widespread transmission among fully vaccinated children. Lancet 1991;338:715-20.

6. Reichler MR, Abbas A, Kharabsheh S, et al. Outbreak of paralytic poliomyelitis in a highly immunized population in Jordan. J Infect Dis 1997;175(suppl 1):S62-S70.

7. Alexander JP, Gary HE, Pallansch M. Duration of poliovirus excretion and its implication for acute flaccid paralysis surveillance: a review of the literature. J Infect Dis 1997;175(suppl 1): S176-S182.

* Member countries are Afghanistan, Bahrain, Cyprus, Djibouti, Egypt, Iran, Iraq, Jordan, Kuwait, Lebanon, Libya, Morocco, Oman, Pakistan, Palestine, Qatar, Saudi Arabia, Somalia, Sudan, Syria, Tunisia, United Arab Emirates, and Yemen.

** The polio eradication initiative is supported by individual countries in which polio is endemic. In addition, external support for the EMR is provided primarily by WHO; United Nations Children's Fund (UNICEF); the governments of Canada, Denmark, Japan, Norway, United Kingdom, and United States (through U.S. Agency for International Development and CDC); and Rotary International.

TABLE 1. Cumulative data for indicators of field and laboratory performance in acute
flaccid paralysis (AFP) surveillance -- Eastern Mediterranean Region, 1995-June 30,
1998
================================================================================================
Indicator                                    1995   1996   1997    1998
-----------------------------------------------------------------------
No. AFP cases                                1727   1779   2878     831
Nonpolio AFP reporting rate*                  0.5    0.7    0.9     0.8
Percentage of AFP cases with virologic        73%    92%    84%     98%
  investigation performed
Percentage of reported AFP cases with         43%    63%    53%     69%
  adequate stool samples+ collected
Total no. stool samples received from        4243   4281   5335    2115
  AFP cases and contacts
Percentage of total samples received          54%    41%    46%     55%
  within 3 days after collection
Percentage of total samples received          93%    94%    91%     92%
  in good condition&
Percentage of total samples                   44%    46%    74%     75%
  reported within 28 days
Percentage of total samples with nonpolio     11%    11%    10%      9%
  enteroviruses isolated
-----------------------------------------------------------------------
* Per 100,000 children aged <15 years. 
+ Two stool samples collected at least 24 hours apart and within 14 days of paralysis onset. 
& Good condition means that on arrival 1) ice or frozen icepacks or a temperature indicator 
  (showing <46 F {<8 C}) is in the container, 2) the specimen volume is adequate (>5 g), 3) no
  evidence of leakage or desiccation is present, and 4) appropriate documentation (laboratory
  request/reporting form) is completed.
================================================================================================

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