Analysis of epidemiological and clinical characteristics of Acute Flaccid Paralyses (AFP) cases in Uganda (1997 – 2004).

Abstract

This study was intended to analyze the epidemiological and clinical characteristics of AFP cases reported in Uganda for the period 1997 to 2004; and to determine whether the establishment of National Polio Expert Committee (NPEC) made a statistical difference on the epidemiological and clinical characteristics of Acute Flaccid Paralyses (AFP) cases reported in Uganda. The study was also intended to establish the incidence of AFP cases for the period 2001 to 2004 under the current surveillance system. The data used was obtained from the Uganda National Expanded Program on Immunization (UNEPI) with consent from the Uganda Virus Research Institute (UVRI), Entebbe.

Using frequency tables, the distribution of AFP cases according to their epidemiological and clinical characteristics was established with respect to NPEC establishment. Selected surveillance indicators were presented in form of averages according to NPEC. These were the time laps for different time periods in AFP surveillance. These included time (lapse1) between date of onset of paralysis and date of investigation, time (lapse2) between the two dates of stool collection, time (lapse3) between date of notification and date of follow–up to examination and time (lapse4) between date of receiving specimens at national level after date of collection. The study further investigated whether associations existed between selected covariates and fitted a model to determine asymmetrical paralysis.

A total of 1,229 AFP cases were reported from 1997 to 2004, in which 39% (474) of the cases were reported before the NPEC establishment and 61% (755) of the cases were reported thereafter. Average time lags for various steps in the process of AFP surveillance and surveillance systems generally improved at each step. For instance, the time (lapse1) between date of onset of paralysis and date of investigation significantly decreased from 21.6 days to just 9.5 days after NPEC establishment and the time (lapse3) between date of notification and date of follow–up to examination significantly decreased from 113.2 days to 78.9 days after NPEC establishment.

AFP cases with asymmetrical paralysis slightly decreased by 7.2% under the current surveillance system (NPEC establishment). More still, cases of under dose OPV increased by 4.6%, while cases of over dose OPV decreased by 8.5%. Further, the proportion of cases in which paralysis progressing in three days of onset increased by 18.8%, while cases of residual paralysis at follow-up increased by 1.9%. Poliovirus strains 1, 2, and 3 were respectively less than 4% before or after NPEC establishment; poliovirus strain 3 had the highest percentage of 3.8% before NPEC establishment. Vaccine-derived strains 1, 2 and 3 respectively were between 0.5% and 3.0% in either era of NPEC. There were no wild poliovirus strains isolated between 1997 and 2004. Non-polio enteroviruses were found to be less than 20% (17.9% before and 18.9% after NPEC establishment) and that conformed to the studies conducted in Australia that showed that non-polio enteroviruses ranged from 15-45% of the AFP cases.

Asymmetrical paralysis was found to have a significant association with region and possession of fever after NPEC establishment. Paralysis progression in three days was also found to have a significant association with possession of fever during NPEC era. Presence of any poliovirus type was found to have a significant association with age group and OPV dose administered. Presence of any vaccine virus type was found to have no significant association with any of the selected variables. Presence of non-polio enteroviruses was found to have a significant association with region and age group, while site of paralysis was found to have a significant association with region, age group, possession of fever and OPV dose.

There is a great need to improve on vaccination culture by routinely sensitizing childcare takers and mothers about the importance of completing OPV dose to their children. AFP follow-ups should be launched immediately after 60 days of onset of paralysis as required by the standards in AFP surveillance and reporting. Avoid using the staff already at the facility; these already have an overload of patients with other illnesses and would not be effective in AFP surveillance and reporting.