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Persistent konzo is low level incidence of konzo that is not associated with konzo epidemics due to drought or war. It has been reported from Mozambique and Tanzania. Various health factors associated with persistent konzo in four villages in Kasanji Health Area, Bandundu Province, DRC were studied, where there were 38 konzo cases in a population of 2283, with mean percentage konzo prevalence of 1.7%. Konzo occurred over the years since 1951 with 0 to 3 cases per year. Anthropometric measurements of children aged 0.5 to 14 y showed that 47% were stunted, 24% underweight, 16% had chronic energy deficiency and 16 to 24% suffered malnutrition. There was no significant difference between children from konzo households or from non-konzo households. The % konzo prevalence (%K) calculated from the equation %K = 0.06 %T + 0.035 %M, where %T = percentage of school children with urinary thiocyanate levels >350 µmol/L and %M = percentage of malnutrition, gave %K = 1.6 from non-konzo households and %K = 2.2 from konzo households, which agrees with the actual mean value of 1.7. However, the equation does not apply when either %T or %M is zero or for very high values of %K > 9.5. The value of %K is nearly twice as sensitive to changes in %T as to changes in %M, which partly explains the greater ease of prevention of konzo by reducing %T to zero, using the wetting method to remove cyanogens from cassava flour, than by reducing %M by broad based methods. Key words: Konzo prevalence, malnutrition, school children, urinary thiocyanate, cassava cyanide.

Konzo is a sudden spastic paraparesis that causes permanent paralysis of the legs and occurs mainly in children and young women. Konzo results from high cyanogen intake and malnutrition caused by a monotonous diet of bitter cassava. The known incidence of konzo in DRC up to 2009 is 3469 cases, but an estimate in 2002 was 100,000 cases. To help resolve this question a konzo survey was made in three health zones in Kwilu District, Bandundu Province, Democratic Republic of Congo (DRC), and the nutrition of those with konzo recorded. Thirty villages (population 22793) in Kwilu District were surveyed for konzo cases, and food consumption scores and mid upper arm circumferences obtained. There were 172 konzo cases with village konzo prevalences of 0.1-17%. The mean konzo prevalence in Masimanimba and Kingandu health zones was much less than in Payikongila health zone, probably because of the higher rate of malnutrition in Payikongila. Since 2009, konzo incidence has increased greatly in Kwilu District and also in 13 villages in nearby Kwango District, where incidence of new konzo cases has been prevented by use of the wetting method. Averaging the data over 495 konzo cases, 48% occurred from 2009 onwards and 52% occurred in the 20+ years before 2009. The very large increase of konzo incidence since 2009 is a public health problem in Bandundu Province, that could be solved by training women to use the wetting method, which removes cyanogens from cassava flour. The wetting method is more direct, effective and cheaper in preventing konzo than broad based interventions. Key words: Konzo survey, cassava, cyanide, nutrition, sulfur amino acids, food consumption score, mid upper arm circumference.

There were 68 konzo cases in three villages in Boko Health Zone, Bandundu Province, Democratic Republic of Congo (DRC), where yearly incidence had increased greatly since 2009. The nine months long intervention to prevent konzo started in the wet season. Village women were taught the wetting method, after which there were no new konzo cases and urinary thiocyanate levels were low. Using data from four different interventions in March 2010, July 2011, September 2013 and the present intervention in October-November 2012, a correlation was found between the monthly cyanide intake (measured by percentage of children with high urinary thiocyanate level) and the monthly konzo incidence. This dose response relationship between cyanide intake and konzo incidence, together with the prevention of konzo in many villages using the wetting method to reduce cyanogen intake, shows that konzo is very likely to be due to high cyanide/low sulfur amino acid intake in a diet of bitter cassava.