Introduction

1.1 History of poliomyelitis and vaccination against poliovirusThe first case of poliomyelitis in Korea was reported in 1939. The inactivated polio vaccine (IPV) and the oral polio vaccine (OPV) were introduced in 1958 and 1962 respectively, and the National Immunization Program (NIP), which was established in 1966, designated poliomyelitis as a second-class communicable disease. Until 1975 most vaccinations used both IPV and OPV, thereafter only OPV was used.The overall risk for vaccine-associated paralytic poliomyelitis is estimated to be approximately one per 2.4 million doses of OPV vaccine [1]. One vaccine-associated paralytic poliomyelitis case was reported in Korea in 2003 [2]. In 2004, the Korea Advisory Committee on Immunization Practices (KACIP) recommended the use of an IPV-only schedule in the NIP, and since then only IPV has been used in Korea.Polio vaccination is recommended at 2, 4 and 6 months of age with a booster dose at 4–6 years. The immunization rate for polio has been sustained at an estimated level of 90–95% since the 1980s.

1.2 Reported cases of poliomyelitis in KoreaAccording to a study conducted during 1962–1964, poliomyelitis cases were most prevalent in one-year-olds, and 70% of the cases were in children below 3 years of age [3]. After polio vaccine was introduced in the 1960s, the incidence of poliomyelitis declined to 0.1/100,000 persons and the mortality rate decreased to 0.1–0.4% [4]. After the five reported cases in 1983, no case of wild poliovirus infection has been reported in Korea up to 2010 (Table 1) [5].

1.3 National infectious disease surveillance and laboratory surveillance systemsAll notifiable vaccine-preventable diseases (VPD) are reported from public health centers, private clinics and hospitals to the Korea Centers for Disease Control and Prevention (KCDC) via a web-based system under the Prevention of Communicable Disease Act. The system is known as the Korea National Infectious Disease Surveillance (NIDS) system.NIDS is coupled with a laboratory surveillance system. Apart from reporting VPD cases to NIDS, for confirmatory testing public health centers, private clinics and hospitals can send various samples from patients suspected of having infectious diseases directly to the Korea National Institute of Health (KNIH) or indirectly through a provincial Research Institute of Public Health and Environment to the KNIH. The results of these tests are reported to the KCDC. A schematic flow chart of the NIDS and laboratory surveillance systems is shown in the Figure.

1.4 Surveillance of acute flaccid paralysisAn annual non-polio rate of acute flaccid paralysis (AFP) of ≥1/100,000 in children under 15 years of age is a requirement for certifying polio eradication in a country [6]. Since 1998, AFP surveillance in Korea has been conducted every year with 70 reporting hospitals under the coordination of the KNIH [7]. As of 2011, 50 sentinel hospitals, including all the pediatrician-training hospitals, are under surveillance.

1.5 Laboratory confirmation of poliomyelitisVirologic evaluation to confirm poliomyelitis consists of tests on two adequate stool specimens from each AFP patient collected 24–48 hours apart and within 14 days of onset of paralysis [8,9]. Laboratory confirmation of poliomyelitis is performed using a cell culture/neutralization test. The stool is further tested using real time reverse transcription polymerase chain reaction (RT-PCR) using pan-enterovirus [9], group-specific [10] and serotype-specific primer sets [11].

Response Plan Against Poliomyelitis OutbreakIn 2010, in response to the increased possibility of poliovirus importation because of a recent poliovirus outbreak in the European region, the Division of VPD Control and NIP of the KCDC prepared a response plan as a guide for key actions to be taken if a poliovirus outbreak occurs in the Republic of Korea.

2.1 Principles

2.2 Action planEach action is not necessarily separate from other actions; rather it is more likely that a number of actions will take place simultaneously. Response teams will be required at all levels of the public health system. The primary response will be driven at the jurisdiction level and coordination at the national level will be overseen by the KCDC.

2.2.1 Reporting suspected case

Any poliovirus isolated from a reported AFP case or any suspected poliovirus infection case reported through the NIDS will signal the immediate initiation of the actions described below.

2.2.2 Case investigation

Within 24 hours of a case being reported an epidemiological investigation will be initiated and, for virologic evaluation, stool specimens from every case will be sent to the national polio laboratory for testing. Epidemiological investigation will determine the likely source of the infection and indicate if the virus might have spread further. It will be essential to collect as much information as possible about the patient’s history including:For an example of the Suspected polio case worksheet see Table 2.

2.2.3 Expert meetings

When the case investigation is complete, the KCDC will convene an urgent meeting of the KACIP sub-committee for DTaP/polio vaccines to inform the advisory group of a possible polio outbreak. The sub-committee will review the results of the case investigation and check that all the necessary information has been obtained. The sub-committee will then decide what further information should be obtained and provide technical advice on what actions should be taken in response to the outbreak. When appropriate, the results of the meeting will be presented to KACIP members.Because a polio outbreak is a public health emergency of international concern under the International Health Regulations (IHR), the IHR Focal Point of Korea will immediately notify the World Health Organization of the situation.

2.2.4 Outbreak response

The poliovirus outbreak response includes:

Case isolation

Individuals identified as or suspected of being infected with poliovirus will be isolated to reduce the risk of virus spread. The patient will be isolated from other patients in hospitals. Weekly stool specimens will be collected from the patient and tested in the national polio laboratory. Isolation can be terminated when two consecutive weekly stool samples are negative for poliovirus.Since poliovirus transmission is mainly person-to-person via the fecal-oral route, health care workers or other caregivers should follow contact precautions.

Management of potential contacts

To contain the spread of the virus, the relevant jurisdiction under the supervision of the higher-level organization will identify potential contacts of a patient and undertake appropriate measures. Potential contacts would be: 1) household contacts who lived with the patient and shared a toilet during the infectious period; 2) health care workers who cared for the patient during the infectious period; and 3) public contacts including toilet contacts who contacted or shared a toilet with the patient before the patient was isolated and the toilet was cleaned.For an example of the Contact tracing worksheet see Table 3.

Immunization

IPV is the only polio vaccine available in Korea, and so IPV will be used in response to an outbreak. All index patient contacts should check their immunization records and update immunization as recommended. Among the contacts, all children and adolescents should be immunized with IPV according to their age. If the vaccination status of a contact is unknown or incomplete, they will be offered a primary series of IPV.Because there is no concrete evidence on the post-prophylaxis effect of the poliovirus vaccine, all those vaccinated will be informed that they are not necessarily protected and that they should still consult a public health center if they develop any symptom.

Cleaning and disinfection

Proper cleaning and disinfecting of areas used by an infected individual is required to prevent onward transmission. Cleaning and disinfecting of every object that might harbor infectious material, including toilets used by the patient during the infectious period, should be diligently carried out. During the isolation of the patient, the stool should be managed properly until it tests negative for poliovirus.

Enhanced surveillance

If a poliovirus outbreak is identified, all virology laboratories in the jurisdiction will be alerted. All clinicians will be immediately informed through various channels, including but not limited to letters or fax, that they are required to participate in the intensified surveillance for AFP. All clinicians should actively encourage children and adolescents to keep up their immunization. Enhanced surveillance should be maintained for a period of at least 6 months after the last case is detected.

Risk communication

Risk communication would include establishing public confidence, providing clear information and rapid and up-to-date announcements to the public. Gaining public confidence is necessary to avoid social disorder and to encourage desirable behaviors, such as immunization and the reporting of any suspicious case.For a sample notification letter see Table 4.

2.2.5 Lessons learned and revision of the plan

At least six months after the last case of poliovirus infection, documentation of the interruption of transmission of poliovirus will be prepared. Detailed and comprehensive documentation describing the epidemiological background, the findings of the case investigations laboratory results, the response to immunization and the results of enhanced surveillance is required.While this documentation is being prepared, all activities in response to the poliovirus outbreak will be reviewed and the reasons why the poliovirus outbreak occurred in the first place will be investigated. All lessons learned will be reflected in a revised national action plan and in improvements in the existing AFP surveillance system.