Etude épidémiologique et spatiale du paludisme en milieu urbain au Sahel : N'Djaména, Tchad

In Chad, malaria is the most important reason for consulting a primary care service. In 2003,
400’152 new malaria cases were reported by public and private health providers
corresponding to 22% of all the health problems notified.
At the example of N’Djaména, Chad. this research presents the spatial and seasonal pattern of
the malaria epidemiology for urban Sahel setting. The objectives are: (1) to determine the
portion of pathologies and specifically febrile pathologies attributable to malaria at the level
of primary care providers, (2) to analyse the quality of care for malaria treatments at the level
of public and private providers with special consideration of inter-personal and technical
dimensions of quality of care, (3) to determine the population based malaria prevalence and
seasonality among children below 5 years.
The approaches proposed consisted in a combination of public health, epidemiological and
geographical methods. Data were collected by:
(1) A longitudinal survey carried out in four health centers (2 in public and 2 private
sectors) to determine the frequency and the seasonality of presumptive malaria
cases; to compare the presumptive and confirmed malaria case frequencies through
blood examination of presumptive malaria cases; the quality of care provided to
presumptive malaria cases at the level of public and private providers through an
observation tool.
(2) Two transversal cluster sample surveys including each one 960 children between 6
months and 5 years, one being carried out at high transmission period (end of the
.rainy season) and a second one at low transmission periods (onset of rainy season)
to determine the seasonality, the prevalence, the spatial pattern of malaria and to
inquire health seeking behaviour for children.
(3) Geographical data collection and management using the remote sensing, the global
positioning and the geographic information systems tools to update the map of
NDjamena, to draw the city boundaries, to geo-reference the health centers and to
produce a buffer of 100, 200 and 300 meters radius around each breeding site.
The results of the longitudinal survey showed that malaria was the first cause of consultation
in N’Djamena. Of a total of 1568 notifications, 703 were attributable to uncomplicated (45%)
and 26 to complicated malaria (1,7%). Based on laboratory examination, 33% of the
presumptive malaria cases in the public health centers and 28% in the private clinics had
some level of parasitaemia. Parasite ratio was high from October to December (44% to 47%),
at the end of the rainy season, and low in March (2%), during the dry and hot season. The
high negative diagnosis rate of the presumptive malaria cases (70%) showed the importance
of an appropriate diagnosis strategy (microscopy, rapid test) development to improve malaria
and other diseases treatment.
The quality care provided to presumptive malaria cases was assessed by direct observation in
the health centers of N’Djamena from June 2002 to March 2003. Interpersonal attributes of
quality of care were better at the level of governmental than private providers, especially with
regard to respects of confidentiality, communication with the patient and explanation of
prescribing and consumption of anti-malarial drugs. Opposite, technical attributes of quality
of care (measurement of temperature, physical examination and spleen palpation) were better
in the private sector. Results indicate the importance to continue to improve incrementally
quality of care, e.g. through regular supervision of the medical staff and continuous education
measures.
Most of the patients of peri-urban primary care providers were living nearby. For example the
63% of patients attending Farcha health center were living close by whereas only 2% were
living in distant places. Opposite most of the patients attending centrally located primary care
providers were coming from the peripheral areas. In particular, 69% of the patients of the
clinic « Providence » were from neigbhourhoods located several kilometers away. Patients
coming from distant areas were mainly adults and people of better socio-economical status.
The results indicate that it would be advisable to re-allocate parts of the available human and
other resources from well equipped, central areas to under equipped, peripheral urban areas.
In view of overcoming the considerable gaps in the knowledge of urban malaria prevalence
and seasonality in the Sahel, two transversal cluster sample surveys were carried out. They
targeted children between 6 months and 5 years. The first survey was done during the high
transmission period (from October to November 2003) and the second during the low
transmission period (from June to July 2004). During the low transmission period for 44% of
the children some kind of sickness was reported, compared to 36% during the high
transmission period. Out of this, presumptive malaria was reported for 35% (119/342) and
42% (174/418) of the children during the high and the low transmission period respectively.
Parasitological diagnosis revealed 27% (259/960) of Plasmodium falciparum parasite ratio
(the only species present) during the high transmission and 6% (54/960) during the low
transmission period. For those presumptive malaria cases reported by the parents and which
did not follow a treatment, the predictive positive value during the high transmission period
was 43% and the attributable fraction (AF) was 38%. For children who received a treatment
the positive predictive value was 24% and the AF was –12%. During the low transmission
period the positive predictive for non treated children was 5% and 3% for those treated and
the AF was –22% and –95% respectively.
These results indicate clearly that malaria among children is only at the end and shortly after
the rainy season an important health problem. Apart from this period, transmission probability
and infection is low. The weakness in the detection of the presumptive malaria by the parents
suggests the strengthening of health education program at community level.
The percentage of children considered sick by their parent varied from 51% in central areas of
N’Djaména to 42% in peri-urban areas. Morbidity attributable to malaria varied from 48% in
the central and peripheral areas to 28% in intermediary zones. Few differences were observed
in spatial distribution of confirmed malaria cases during the high transmission period. The
overall Plasmodium falciparum prevalence by geographic area was 29% in central zones,
23% in intermediary zones and 28% in peri-urban zones. On the over hand during the low
transmission period Plasmodium falciparum parasite ratio in the intermediary zones (8%) and
central zones (7%) were higher than in the peri-urban zones.
Uncomplicated malaria treatment was mainly done at home and only one therapeutic itinerary
was chosen. On 176 children who suffer from the malaria since more than 5 days 51% had
been treated at home, 36% were taken in a health centre and 13% were not maintained.
Chloroquine was the fundamental treatment against malaria which was given at home (28%).
The dosage was effective in more than 86% of the cases. The biggest part of the therapeutic
products which were used at home came from small shops or markets of the district. Very
little were bought in a pharmacy, pharmaceutical depot (21%) or in a health centre (9%).
Malaria transmission is seasonally but not spatially heterogeneous in N’Djamena. Indeed
results of this research show that malaria prevalence rates are not higher in peri-urban areas
leading to additional needs for inquiry on spatial malaria transmission characteristics in
Sahelian urban settings. Furthermore, this research showed that clinical diagnosis of malaria
at the level of health providers as well as households has low positive predicted values. The
low specificity of clinical diagnosis as well as self-diagnosis at household level leads to
inappropriate care for a large proportion of patients and has a major impact on economic costs
on health services and households. Therefore, it is urgent to revisit current diagnostic
approaches for the first contact level in Sahelian settings. Improving clinical skills of the
personnel and the households on malaria is highly desirable, but will not be sufficient to overcome
misdiagnosis. The systematic use of microscopy-based diagnosis and/or rapid
diagnostic tests should be considered to appropriately manage malaria as well as non-malaria
cases. It vary according to the time period and the environment of the population. These
factors are important in the elaboration of locally adapted malaria control strategies in the
Sahelian urban setting.