Canadian Paediatric Surveillance Program - 2003 Results

CPSP Principal Investigators

Surveillance studies in 2003
New studies in 2004

 

Surveillance Studies in 2003

Acute flaccid paralysis

(January 1996 to December 2004)

Highlights

• No wild polio cases have been isolated in Canada since 1988.
  
• The number of AFP cases reported for 2003 and 2002 was lower than in previous years; however, duplicate reporting remains high.
  
• Guillain-Barré syndrome accounts for at least 74% of confirmed AFP cases.
  
• Polio viral stool cultures are still essential.
  

Background

The elimination of indigenous wild poliovirus transmission in Canada, and the rest of the American region, was certified in September 1994. However, until global polio eradication is attained, there remains an ongoing risk of wild poliovirus importation from polio-endemic regions to Canada. Consequently, active surveillance of acute flaccid paralysis (AFP) in children less than 15 years old is used to monitor potential cases of paralytic poliomyelitis. Based on World Health Organization (WHO) criteria for AFP surveillance (Table 5), the estimated minimum number of cases in Canada is 58 per year. AFP surveillance in Canada was initiated in 1991 through the IMPACT (Immunization Monitoring Program ACTive) network of paediatric tertiary-care centres and, since 1996, has been implemented through the CPSP. This report presents the results of AFP surveillance in 2003 and compares them to those from previous years.

Objective

The objective of AFP surveillance is to identify AFP cases (including Guillain-Barré syndrome [GBS]) in children less than 15 years of age to rule out paralytic poliomyelitis and thereby monitor the polio-free status of Canada.

TABLE 5 World Health Organization quality assurance criteria for acute flaccid paralysis surveillance
1) one case per 100,000 in a population less than 15 years of age
2) adequate polio virus stool culture in 80% of cases

Case definition

Acute onset of focal weakness or paralysis characterized as flaccid (reduced tone) without other obvious cause (e.g., trauma) in children less than 15 years of age. Transient weakness (e.g., post-ictal weakness) should not be reported.

Results and discussion

In 2003, the CPSP received 84 initial AFP reports, of which 42 (50%) were confirmed cases. The other half were split between 35 duplicate reports and seven cases that did not meet the AFP surveillance case definition or have adequate information. Forty-two confirmed cases represents a rate of 0.72% per 100,000 which is below the minimum estimated background rate of one case per 100,000 children less than 15 years of age, or 58 cases. With the anticipated ‘late reports' for the current year, the final number is likely to be slightly higher, but below the WHO targeted rate. Cases ranged in age from two months to 15 years (median 5.9 years, mean 7.3 years) in 2003. Table 6 shows the age distribution of AFP cases reported in 2003 compared with cases reported from 1996 to 2002. Overall, the age distribution is similar throughout the reporting period. More than two-thirds (69%) of cases were males.

Although most Canadian children today are vaccinated against polio, only 29 of the 42 cases (69%) had documentation of routine childhood immunization, and all had received age-appropriate polio immunization. For the remaining 13 cases, no polio vaccine-specific information was available on the detailed case report forms.

Virological investigation for polio or other enteroviruses

A total of 20 cases (48%) had stool examination; virology was not done or the status was unknown for 22 cases (52%). However, adequate stool investigation for the isolation of poliovirus or non-polio enteroviruses (i.e., stool specimen collected within two weeks of the onset of paralysis) was reported for only 17 of 42 cases (40%). For three additional cases, although stool specimens were collected, it was after two weeks of onset of paralysis. None were positive for polioviruses; one was characterized as ‘adenovirus' and another as ‘echovirus'. None of the nine throat and/or 23 cerebrospinal fluid specimens collected for viral isolation was positive for poliovirus. For 17 of the 42 cases (40%), stool specimens were also tested for Campylobacter organisms; but all were negative.

Neurological investigations consisted of at least one or more of the following:

CSF abnormalities (protein, glucose, WBC, neutrophils, lymphocytes, and RBC), nerve conduction studies, electromyography, MRI or CT scan; abnormal findings compatible with the neurological diagnosis were reported for one or more of the tests done. Twenty-six (72%) of the 36 CSF specimens indicated some abnormal findings. MRI or CT scanning was done for 37 cases (88%); for MRI, 14/21 or 67% showed some abnormality. Electromyography and/or nerve conduction studies were done for 33 cases; 26 (79%) of which had abnormal findings. Guillain-Barré syndrome was the final neurological diagnosis in 31 cases or 73.8% (one was a GBS Miller-Fisher variant) and transverse myelitis in four (9.6%) (Table7). The remaining seven diagnoses included acute disseminated encephalomyelitis (3), lumbosacral plexineuropathy (1), progressive ischemic myelopathy (1), encephalomyelitis radiculitis (1), and post-infectious transverse myelitis (1).

Forty-one of the 42 required hospitalization for periods ranging from one to 105 days (mean of 17 days); seven cases were hospitalised for 30 days or longer. Of the 42 cases, two (4.8%) recovered fully, 29 (69%) recovered partially with residual weakness, and 11 (26. 2%) had an unknown recovery status at 60 days after the onset of paralysis.

None of the clinical specimens tested, i.e., stool, nasopharyngeal or cerebrospinal fluids, were positive for poliovirus infection.

TABLE 6 Age distribution of AFP cases reported to the CPSP, 1996-2003
Age group (years)	Number of cases (%)
	1996	1997	1998	1999	2000	2001	2002*	2003
0 - 1	2 (6.7)	-	2 (4.6)	3 (4.9)	2 (3.3)	8 (14.8)	10 (23.3)	5 (11.9)
2 - 5	11 (36.7)	13 (37.1)	15 (34.1)	18 (29.5)	24 (39.3)	18 (33.3)	16 (37.2)	17 (40.5)
6 - 10	9 (30.0)	12 (34.3)	18 (40.9)	23 (37.7)	22 (36.1)	14 (25.9)	11 (25.6)	7 (16.7)
11 -< 15	8 (26.6)	10 (28.6)	9 (20.4)	17 (27.9)	13 (21.3)	14 (25.9)	6 (13.9)	13 (30.9)
Total	30 (100)	35 (100)	44 (100)	61 (100)	61 (100)	54 (100)	43 (100)	42 (100)

TABLE 7 Neurological diagnosis of AFP cases reported to the CPSP, 1996-2003
Final Diagnosis	Number of Cases (%)
	1996	1997	1998	1999	2000	2001	2002*	2003
Polio	0	0	0	0	0	0	0	0
Guillain-Barré syndrome	21 (70.0)	29 (82.8)	34 (77.3)	50 (82.0)	49 (82.0)	42 (77.7)	33 (76.7)	31 (73.8)
Transverse myelitis	6 (20.0)	2 (5.7)	6 (13.6)	7 (11.5)	4 (6.6)	8 (14.8)	7 (16.3)	4 (9.6)
Encephalitis/ encephalomyelitis/ encephalopathy	1 (3.3)	1 (2.9)	—	—	—	—	—	3 (7.1)
Myelopathy	—	1 (2.9)	—	—	—	—	—	—
Radiculopathy /radiculoneuritis	1 (3.3)	1 (2.9)	—	—	—	1 (1.9)	1 (2.3)	—
Plexitis/ lumbosacral plexitis	—	—	—	2 (3.2)	—	—	—	1 (2.4)
Brachial neuritis	—	—	—	1 (1.6)	—	—	—	—
Rhombomyelitis	—	—	—	1 (1.6)	—	—	—	—
Other	—	—	—	—	8 (13.1)	3 (5.6)	2 (4.7)	3 (7.1)
Not specified /undetermined diagnosis or etiology	1 (3.3)	1 (2.9)	3 (6.8)	—	—	—	—	—
Total	30 (100)	35 (100)	44 (100)	61 (100)	61 (100)	54 (100)	43 (100)	42 (100)

* Includes four delayed reports not included in the CPSP 2002 Results.

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