An Epidemiologic Investigation of Potential Risk Factors for Nodding Syndrome in Kitgum District, Uganda

<div><p>Introduction</p><p>Nodding Syndrome (NS), an unexplained illness characterized by spells of head bobbing, has been reported in Sudan and Tanzania, perhaps as early as 1962. Hypothesized causes include sorghum consumption, measles, and onchocerciasis infection. In 2009, a couple thousand cases were reportedly in Northern Uganda.</p><p>Methods</p><p>In December 2009, we identified cases in Kitgum District. The case definition included persons who were previously developmentally normal who had nodding. Cases, further defined as 5- to 15-years-old with an additional neurological deficit, were matched to village controls to assess risk factors and test biological specimens. Logistic regression models were used to evaluate associations.</p><p>Results</p><p>Surveillance identified 224 cases; most (95%) were 5–15-years-old (range = 2–27). Cases were reported in Uganda since 1997. The overall prevalence was 12 cases per 1,000 (range by parish = 0·6–46). The case-control investigation (n = 49 case/village control pairs) showed no association between NS and previously reported measles; sorghum was consumed by most subjects. Positive onchocerciasis serology [age-adjusted odds ratio (AOR₁) = 14·4 (2·7, 78·3)], exposure to munitions [AOR₁ = 13·9 (1·4, 135·3)], and consumption of crushed roots [AOR₁ = 5·4 (1·3, 22·1)] were more likely in cases. Vitamin B6 deficiency was present in the majority of cases (84%) and controls (75%).</p><p>Conclusion</p><p>NS appears to be increasing in Uganda since 2000 with 2009 parish prevalence as high as 46 cases per 1,000 5- to 15-year old children. Our results found no supporting evidence for many proposed NS risk factors, revealed association with onchocerciasis, which for the first time was examined with serologic testing, and raised nutritional deficiencies and toxic exposures as possible etiologies.</p></div

Frequency of nodding syndrome cases and village controls with positive exposures or presence of clinical findings.

<p>Statistically significant values are in bold.</p><p>CI: Confidence interval. OR: odds ratio.</p>*<p>Percent with exposure is calculated by number of cases with a positive exposure divided by number of cases, or number of controls exposed divided by number of controls.</p>‡<p>Odds ratio calculated as odds of positive exposure in cases versus odds of exposure in controls.</p>†<p>AOR₁: Odds ratio adjusted for age. Note: additional models 2 (adjusted for age, munitions, roots) and 3 (adjusted for age, measles, sorghum, onchocerciasis skin snip positive) are available in an online appendix Table 5.</p>?<p>Missing data existed for the following exposure variables: malaria, malnutrition, pneumonia, diarrhea, head injury, crushed leaves, roots, flowers, inhaled medicine (number of cases responding to question = 50); swimming in the river or pond, visual or auditory hallucinations (cases = 49); skin nodules (cases = 48); low height for age, low BMI for age (cases = 45, controls = 48); all data used for frequencies, data from available matched pairs used for matched analyses.</p>+<p>Firth’s correction.</p>**<p>low BMI-for-age z-score: <−2 SD, an indicator of acute malnutrition; low height-for-age z-score: <−2SD, chronic malnutrition.</p><p>Unadjusted and adjusted odds of positive exposure or clinical finding in a case versus control.</p

Prevalence and mean socio-demographic characteristics of nodding syndrome case patients and control subjects aged 5 to 15 years in Kitgum District, Uganda.

∧<p>51 total cases were enrolled; 49 matched to 49 village controls, and 44 matched to 44 household controls.</p><p>McNemar’s, Stuart’s <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066419#pone.0066419-Agresti1" target="_blank">[27]</a>, and paired t tests were performed to obtain significance level.</p>*<p>p<0.05.</p>**<p>p<0.001.</p

Case definitions for persons with Nodding Syndrome. Criteria 1–2 were required^∧ for surveillance purposes and 1–5* were required for enrollment in the case-control investigation.

∧<p>as determined by Uganda Ministry of Health and WHO epidemiologists.</p>*<p>as determined by CDC medical epidemiologist.</p

Epidemic curve depicting time course of disease onset: cases identified by surveillence and case-control studies in Kitgum District plotted by reported NS onset year.*.

<p>Epidemic curve depicting time course of disease onset: cases identified by surveillence and case-control studies in Kitgum District plotted by reported NS onset year.*.</p

Comparison of laboratory findings among nodding syndrome cases and village controls, frequency for positive results or high value unless otherwise denoted by “^*”, unmatched unadjusted and age-adjusted odds of an abnormal laboratory value^∧, ^†, ^¶ in a case.

*<p>indicates values that where “low” or below normal cut off values and signifies an abnormal test result.</p>∧<p>Cut off values for positive infectious disease results: onchocerciasis skin snip>0, onchocerciasis Ov16 ELISA >0·1, onchocerciasis OvFAR/−MSA LIPS >7000 (negative<5000) cysticercosis >0, trypanosomiasis >0, hepatitis E >0·22 (Hep E IgM/G was considered reactive if either IgM or IgG was >0·22), measles PCR >0.</p>†<p>Low values for nutrition results: vitamin B6<20 nmol/L, B12<200 pg/mL, A <20 µg/dL, Hb 12 g/dL, folate <317 nmol/L.</p>¶<p>Normal reference ranges: ALT 5·3–43·3 U/l, AST 0–37 U/l, ALP 98–279 U/L, CREA 0·5–1·2 mg/dl, UREA 10–50 mg/dl, TBIL 0–1 mg/dl, copper 60–249 µg/dL, selenium 113–130 µg/L, zinc 70–120 µg/dL, mercury 0·42–3·19 µg/L, thiocyanate <2100 ng/ml (zero cases and controls had toxic levels >14000 ng/ml); CSF protein 15–45 mg/dL; CSF glucose 40–70 gm/dL.</p>**<p>AOR: Odds ratio adjusted for age.</p>∧∧<p>LIPS – <i>Luciferase immunoprecipitation system.</i></p>††<p>CATT – Card Agglutination Test with Stained Trypanosomes.</p>¶¶<p>HPLC – High-performance liquid chromatography.</p>***<p>HPLC-UV/VIS – <i>HPLC method with ultraviolet-visible spectrophotometry detection.</i></p>∧∧∧<p>Multiplex PCR tests for 35 groups of family, subfamily or genus nucleic acid targets, covering 19 families of viruses.</p>†††<p>Case mf density mean = 39·1 (range 0–204); control mf density = 5·8 (range 0–60).</p>¶¶¶<p>Matched unadjusted and age-adjusted odds were also performed on labs found to have significant associations: O. volvulus Ov16 OR = 3.33 (1.34, 8.30) and AOR = 3.16 (0.84, 11.89), O. volvulus OvFAR/−MSA OR = 17.00 (2.26, 127.74) and AOR = 20.80 (1.37, 316.24).</p