Poliomyelitis
Poliomyelitis is an acute illness which may result from invasion of the gastro-intestinal tract by one of three types of polio virus. It usually affects small children under the age of three years. The virus is transmitted through contaminated food and water, and multiplies in the intestine, from where it can invade the nervous system. Transmission occurs through contact with faeces or pharyngeal secretions of an infected person. The incubation period ranges from three to 21 days, but may be longer. Cases are infectious from about ten days before to seven days after the onset of symptoms; however, carriers and some immuno-compromised persons may shed the virus in faeces for longer than six weeks (Howard, 2005).
Most infections are not clinically apparent; up to 95% of infections are asymptomatic (CDC, 2009).
Risk of complications
Clinical disease may range in severity from minor illness (abortive poliomyelitis), to non-paralytic poliomyelitis (aseptic meningitis) and paralytic poliomyelitis (Feigin, 2009).
Approximately 48% of polio infections consist of a non-specific minor illness without clinical or laboratory evidence of central nervous system invasion (CDC, 2009; Feigin, 2009). This clinical presentation is known as abortive poliomyelitis, and is characterised by complete recovery in less than one week (CDC, 2009).
Nonparalytic aseptic meningitis (symptoms of stiffness of the neck, back, and/or legs) which usually follows several days after a prodrome similar to that of a minor illness, occurs in 12% of polio infections (CDC, 2009). Increased or abnormal sensations can also occur. Typically these symptoms will last from two to ten days, followed by complete recovery (CDC, 2009).
Less than 1% of all polio infections result in flaccid paralysis (CDC, 2009; Heymann, 2004). Paralytic symptoms generally begin one to ten days after prodromal symptoms and progress for two to three days. Generally, no further paralysis occurs after fever subsides (CDC, 2009). Many patients with paralytic poliomyelitis recover completely and, in most of them, muscle function returns to some degree. Weakness or paralysis 12 months after onset is usually permanent (CDC, 2009).
In acute flaccid paralysis (AFP), the legs are usually more often affected than the muscles of the upper body. However, the polio virus may invade the brain stem, potentially leading to breathing difficulty and even death. Symptoms include headache, gastro-intestinal disturbance, malaise and stiffness of the neck and back, with or without paralysis (American Academy of Pediatrics, 2006; Shibuya & Murray, 2002). Improvements are seen within the first six months (Farbu, 2013; Neumann, 2004). The principal complication is painful, acute, asymmetric paralysis of the arms or the legs, reaching its maximum extent over the course of three to four days and leading to permanent lameness of the affected limbs and breathing difficulties (UK Department of Health, 2006; WHO, 2014).
Given the estimates of symptomatic polio cases, we considered that on average 8.5% of infections are symptomatic (611%; CDC, 2011); hence 70.59% of cases on average will be abortive (uncomplicated), 17.65% will be non-paralytic and 11.76 will be paralytic.
According to WHO (WHO, 2014), 1 in 200 infections leads to irreversible paralysis. Given that 1% of all infections has a paralytic form, we considered that 50% of all paralytic forms would develop a permanent disability due to paralysis.
Post-polio syndrome is a long-term sequela that occurs 3035 years after infection in approximately 2550% of cases (Jubelt & Drucker, 1999). A slowly progressing condition, it can also occur in patients who have had the non-paralytic form of poliomyelitis. The most common symptoms include slow, progressive muscle weakness, fatigue (both generalised and muscular) and a gradual decrease in the size of muscles (muscle atrophy). Pain from joint degeneration and increasing skeletal deformities such as scoliosis (curvature of the spine) is common and may precede the weakness and muscle atrophy. Some individuals experience only minor symptoms while others develop visible muscle weakness and atrophy. Fatigue is clearly the most prominent manifestation, occurring in up to 80% of patients (Jubelt & Drucker, 1999). Post-polio syndrome is rarely life-threatening (NINDS, 2012).
Case fatality proportion
The case fatality proportion is 510% of paralytic forms (WHO, 2014).
Model input summary
Table 1. Transition probabilities used in the outcome tree
Health outcome |
Distribution of health states in health outcome |
Transition probability |
Source/assumption |
Symptomatic infection (Uncomplicated) (Non-paralytic poliomyelitis) (Paralytic poliomyelitis) |
70.59% 17.65% 11.76% |
6-11%
|
CDC, 2009 CDC, 2009; Heymann, 2004 |
Post-polio syndrome |
|
2550% |
Jubelt & Drucker, 1999 |
Permanent disability following paralytic poliomyelitis |
|
50% |
WHO, 2014 |
Fatal cases following paralytic poliomyelitis |
|
5-10% |
WHO, 2014 |
Table 2. Disability weights and duration
Health
outcome |
Disability Weight (DW) (Haagsma, 2015) |
Duration |
||
DW |
Label |
In years |
Source |
|
Symptomatic infection (Uncomplicated) (Non-paralytic poliomyelitis) (Paralytic poliomyelitis) |
0.007 (0.0050.01) 0.051 (0.0390.06) 0.125 (0.1040.152) |
Infectious disease, acute episode, mild Infectious disease, acute episode, moderate Infectious disease, acute episode, severe |
0.019 0.0050.027 0.0110.038 |
CDC, 2009 CDC, 2009 CDC, 2009 |
Permanent disability following paralytic poliomyelitis |
0.067 (0.0540.081) |
Spinal cord lesion below neck level (treated) |
Remaining life expectancy |
|
Latency period before PPS |
0 |
|
3035 |
Jubelt & Drucker, 1999 |
Post-polio syndrome (PPS) |
0.344 (0.30.391) |
Musculoskeletal problems, generalised, moderate |
Remaining life expectancy |
|
References
American Academy of Pediatrics. Red Book: 2006 Report of the Committee on Infectious Diseases. 27th ed. Elk Grove Village. 2006.
Centers for Disease Control and Prevention (CDC). Epidemiology and Prevention of Vaccine-Preventable Diseases. Atkinson W, Wolfe S, Hamborsky J, McIntyre L, eds. 11th ed. Washington DC: Public Health Foundation, 2009.
Department of Health, UK. Immunisation against infectious disease (the Green Book). 3rd ed. London: The Stationery Office. 2006.
Feigin R, Cherry J, Demmler-Harrison GJ, Kaplan S. Feigin and Cherry's Textbook of Pediatric Infectious Diseases. Sixth Edition, 2009.
Farbu E. 2013. Post-polio Syndrome. In: JH Stone, M Blouin, editors. International Encyclopedia of Rehabilitation. Available online: http://cirrie.buffalo.edu/encyclopedia/en/article/138/
Haagsma JA, Maertens de Noordhout C, Polinder S, Vos T, Havelaar AH, Cassini A, Devleesschauwer B, Kretzschmar ME, Speybroeck N, Salomon JA. Assessing disability weights based on the responses of 30,660 people from four European countries. Population Health Metrics 2015; 13: 10
Heymann D, Aylward B. Poliomyelitis. Orphanet Encyclopedia. WHO. 2004.
Howard RS. Poliomyelitis and the post polio syndrome. BMJ 2005;330(7503):13141318.
Jubelt B, Drucker J. Poliomyelitis and the Post-Polio Syndrome in Motor Disorders. Philadelphia: Lippincott Williams and Wilkins. 1999. pp. 381.
Neumann D. Polio: its impact on the people of the United States and the emerging profession of physical therapy (PDF).The Journal of Orthopaedic and Sports Physical Therapy 2004; 34 (8): 47992. PMID 15373011
Post-Polio Syndrome Fact Sheet. NINDS. 2012.
Shibuya K, Murray CJL. Poliomyelitis. In: Stein CE, Murray CJL, Lopez AD (eds). The Global Burden of Disease and Injuries Series, Volume 4: The Global Epidemiology of Infectious Diseases. WHO, 2002.
UNICEF Executive Board Special (2009). Focus Session on Global Health, with particular focus on polio eradication. Available online from: http://www.unicef.org/about/execboard/files/Special_focus_session-Background_SFS_English_8_June_09(1).pdf
World Health Organization (WHO). Poliomyelitis. Available from http://www.who.int/topics/poliomyelitis/en/ [accessed 19 September 2014].