Spatio-temporal patterns of meningococcal meningitis in Burkina Faso, Mali and Niger

and relationships to climate

Sylwia Trzaska1, Pietro Ceccato1, Judy Omumbo1, Michael Bell1, Madeleine Thomson1, Mamoudou Djingarey2, Sassan Noazin3,

Isabelle Jeanne4

1 The International Research Institute for Climate and Society, Columbia,University, Palisades, NY USA2 Multidisease Surveillance Center, Ouagadougou, Burkina Faso3 World Health Organization4 CERMES, Niamey, Niger

Meningitis vaccine programme

Rationale

Identify which environmental factors can be used as predictors to Meningitis outbreaks in order to develop an Early Warning System based on forecast and monitoring products of the environmental factors.

Data and Methods Meningitis Original data for Central Sahel collected by WHO incidence weekly, district level• Niger - 42 distr., 1986-2005• Mali - 58 distr., 1994-2005• Burkina Faso – 55 distr., 1997-2005

AtmosphereNCEP Reanalysis (surface)

• Daily aggregated to weekly• 1949-present • Coarse resolution (2.5x2.5) but global• Consistency among variables

DustTOMS/EPTOMS

• Daily aggregated to weekly• 1996-2004• Resolution 1.5x1

Objective definition of spatial and temporal scales for meningitis incidence variability via statistical analyses

Investigation of potential large scale atmospheric predictors

All countries,1997-2005

Weeks 5-20, standardized 4 classes

-0.5

0

0.5

1

1.5

2

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Class 1

Class 2

Class 3

Class 4

Meningitis Mean Seasonal Cycle

Cluster Analysis

Earlier onset and termination of meningitis season in southern districts Northward progression of the epidemic season

Environmental Factors

E.g. Week 13 Maximum temperature,Specific Humidity, Wind

-0.5

0

0.5

1

1.5

2

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Class 1

Class 2

Class 3

Class 4

• Northaward progression of Meningitis linked to highest temperatures, in the region of convergence between Harmattan and southwesterlies• Highest dustiness (not shown)• NOT lowest humidity

•Termination linked to arrival of moister, cooler and cleaner air

Environmental Factors

E.g. TOMS w 1-20

• Northaward progression of Meningitis linked to highest temperatures, in the region of convergence between Harmattan and southwesterlies• Highest dustiness (not shown)• NOT lowest humidity

•Termination linked to arrival of moister, cooler and cleaner air

Interannual variabilityStandardized Annual Incidence Anomalies

3 distinctive spatial structures: uniform epidemics, E/W dipole, Center vs E&W

High incidence

Low incidence

Missing data

Niger – Interannual Variability, EOF

Niger – Interannual Variability,

atmosphere

Conclusions Seasonal Cycle

District Scale - northward progression of the epidemics

Links to surface atmospheric conditions - epidemic season coincides with highest Tmax and dust in the low level wind conv.- moves northward with the seasonal cycle- epidemic season terminates when high humidity/low dust air mass reach the region

Consistent with previous studies Future: Establish thresholds

Interannual variability

Can be approached from annual (or peak) cumulative incidence values for each district

Differences in control strategies do not hinder spatial features- large scale epidemic/non epidemic years- dipolar structures (E vs W), not related to boundaries

Insufficient length of data for establishing robust results

Niger: climatic signal – potential for prediction- for epid./non-epid. years: climatic anomalies in equatorial and S Atlantic- for dipolar years: reversed anomalies between N Tropical Atlantic and Central Sahel

Future: Further predictability studies

NigerDistrict Level

Establish thresholds for dust, tmax, wind

Interannual variability

Niger – 20 years of record

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Class 1

Class 2

Class 3

Class 4