Malaria morbidity and temperature variation in a low risk Kenyan district: A case of overdiagnosis
Malaria is a leading cause of morbidity and mortality inrnsub-Saharan Africa with 90 of all global deaths due tornmalaria occurring in this region Snow et al. 2003 WorldrnHealth Organisation 2003. Treatment of malaria has for arnlong time been characterised by overtreatment at healthrnfacilities and undertreatment at the community and household levels. A review by Amexo et al. 2004 found thatrnclinical diagnosis by health professionals overestimatesrnmalaria number of cases with negative microscopy overrnthe number of malaria clinical diagnosis by an average ofrn61 ranging from 28 to 96. Climatic factors likerntemperature rainfall and relative humidity influencerntransmission of malaria. Temperature is a major determinantrnespecially in cool areas such as the highlands. These regionsrnreceive abundant rainfall but the relatively low temperaturernhinders the proliferation of the female anopheline vector. InrnSouth Africa Craig et al. 2004 analysed malaria case data forrn30 years in KwaZulu-Natal and identified a significantrncorrelation between mean maximum daily temperature fromrnJanuary to October of the preceding season and the numberrnof malaria cases. A study in Burkina Faso found that of thernmeteorological factors associated with clinical malaria meanrntemperature had the largest effect. These authors went on tornrecommend integration of temperature data in routine healthrninformation systems for assessment of the malaria transmission link Y et al. 2007. The present study looks at cases ofrnInt J Biometeorol 2009 53:299304rnDOI 10.1007/s00484-009-0216-5rnJ. Njuguna rnNyandarua District Public Health OfficernP.O. Box 86-20300 Nyahururu Kenyarne-mail: jowanju2002yahoo.comrnJ. MuitarnNyahururu District Hospital LaboratoryrnP.O. Box 86-20300 Nyahururu KenyarnG. MundiarnNyandarua District Health Information OfficernP.O. Box 86-20300 Nyahururu Kenyarnmalaria reported over a period of 4 years together withrntemperature and rainfall data over the same period.
Malaria outpatient cases for 4 years 20032006 werernanalysed on a monthly basis and the means determined.rnEach health facility in the district is required to submit arnmonthly tally sheet of all outpatient cases treated. Malariarncases were extracted from these sheets to compile thernmonthly malaria burden. Data on mean maximum temperature and mean daily rainfall for each month for the yearsrn20032006 were provided by the Nyahururu meteorologyrndepartment. Analysis was done using MS Excel 2003 andrnSPSS version 11
The mean number of monthly cases for the 4-year periodrnwas 8313. July had the highest mean number of casesrn12151 followed by August June and April Table 1.rnThese 4 months account for 40.7 of all reported cases.rnAcross the 4 years cases have been constantly on the risernduring the months of June and July whereas August andrnMarch reported upsurges followed by declines. DecemberrnJanuary and April had the fewest cases. The monthly meanrnmaximum temperature for the 4-year period was 21.7 C.rnFebruary and March had the highest temperature both atrn24.2 C. July had the lowest temperature at 20.1 Crnfollowed by August and June at 20.2 and 21.1 Crnrespectively.rnMalaria cases have generally been on the rise. Betweenrn2003 and 2004 there was a 59.6 increase in malariarncases from a mean of 5178 to 8267 and an increase ofrn0.09C in mean maximum temperature. There was anotherrnincrease of 22.6 in malaria cases from 2004 to 2005 to arnmean of 10138 cases and an increase of 0.44 C in meanrnmaximum temperature. There was a slight decline of 0.05rnin malaria cases to a mean of 9673 and a decline in meanrnmaximum temperature by 0.44 C.rnAs can be seen in the graph in Fig. 2 malaria cases tend tornrise from January and peak slightly in March. In April theyrndecline before gradually rising and peaking in July. This isrnthen followed by another decline. In 2004 cases peaked inrnAugust instead of July. Temperatures tend to rise fromrnJanuary and peak in February and March which have thernTable 1 Malaria morbidity mean maximum temperature and mean daily rainfall 20032006rnMonth Number of malaria cases of all cases Mean monthly temperature C Mean daily rainfall mmrnJanuary 6994 6.7 22.2 1.1rnFebruary 7388 7.4 24.2 0.7rnMarch 8445 8.5 24.2 2.0rnApril 7069 7.1 22.2 4.0rnMay 8160 8.2 21.7 3.2rnJune 9737 9.8 21.1 2.9rnJuly 12151 12.2 20.1 4.3rnAugust 10200 10.2 20.2 4.9rnSeptember 8239 8.3 21.6 2.3rnOctober 7727 7.8 21.8 1.2rnNovember 7347 7.4 20.4 2.6rnDecember 6304 6.3 21.2 2.0rnInt J Biometeorol 2009 53:299304 301rnhighest temperatures. Then a gradual decline follows untilrnJuly. A rise follows in September and October and a declinernin November followed by another rise in December.rnNyandarua district receives abundant rainfall throughoutrnthe year. There was only 1 month across the 4 years when itrndid not rain namely February 2003. Highest rainfall isrnrecorded in August July April and May. Rainfall follows arngeneral pattern of rising from February and peaking inrnApril followed by a slight decline and a further peak inrnAugust. This is followed by a decline and a slight peak
The majority of malaria cases occur in June July andrnAugust which also have the lowest mean temperatures ofrn21.1C 20.1C and 20.2 C respectively. July and Augustrnalso have the highest rainfall. The effects of temperature onrntransmission are many but its specific effect on sporogonicrnduration development of the malaria parasite within thernmosquito and mosquito survival is the most importantrnOnori and Grab 1980. Below 18C transmission isrnunlikely because few adults0.28 survive the 56 daysrnrequired for sporogony at that temperature and becausernmosquito abundance is limited by long larval duration. Atrn20C sporogony takes 28 days with only 5.6 of vectorsrnsurviving after this period as the life span of anophelesrngambiae is 21 days. At 22C sporogony is completed inrnless than 3 weeks and mosquito survival is sufficiently highrn15 for the transmission cycle to be completedrnRainfall is important as it provides the essential breedingrnsites for the mosquito vectors. However the relationshiprnbetween mosquito abundance is complex and best studiedrnwhen temperature is not limiting Snow et al. 1999. Inrnareas of low temperatures such as the highlands whichrnexperience high rainfall it is the temperature element thatrnhinders the mosquito from breeding proficiently. Like JulyrnApril also experiences high rainfall. It has a meanrnmaximum temperature of 22.2C compared to 20.1C forrnJuly. It can be estimated that 15 of vectors survive inrnApril compared to 5.6 in July. Thus more cases should bernreported in April or May due to a lag effect. April accountsrnfor 7.1 of all cases and May 8.2 compared to 12.2 forrnJuly. June has relatively low temperatures meaning that thernlikelihood of July benefitting from a lag effect is minimal.rnA study by Y and colleagues found that the risk ofrnclinical malaria increased with an increase in mean temperature up to 27C Y et al. 2007. In Zimbabwe it was foundrnthat mean monthly temperature range 2832C maximumrntemperature 2428C and high rainfall promote seasonalrntransmission of malaria Mabaso et al. 2005.rnA possible explanation for the coldest months having thernhighest number of malaria cases could be due to overdiagnosis of malaria cases. In Nyandarua district respiratory tract infections are the leading cause of outpatientrnmorbidity. During these cold rainy months cases ofrnrespiratory infections tend to increase as they are temperature dependent Fodha et al. 2004. It has been shown thatrnthere is an increased risk of contracting respiratoryrninfections in the rainy season among children Roca et al.rn2006. Some of these cases could be misdiagnosed orrnmisclassified as malaria. A study in Mozambique found thatrnmalaria was strongly associated with an increased risk ofrnrespiratory infections Roca et al. 2006. A prospectivernstudy in a meso-endemic area in Uganda found malaria tornbe responsible for only 32 of new febrile cases amongrnchildren. The other febrile cases with negative blood smearsrnwere attributed to diseases like upper respiratory infectionrncommon cold and non-specified fever Meya et al. 2007. Itrnhas also been shown that the symptoms of malaria tend tornoverlap with those of pneumonia ODempsey et al. 1993rnand one Ugandan study found 30 of children hadrnsymptom overlap necessitating dual treatment Kallanderrnet al. 2004.
These coldrnmonths also tend to have the highest number of cases ofrnrespiratory infections. There is a possibility that some of thesernwere misdiagnosed as malaria based on the fact that only arnsmall proportion of malaria cases were diagnosed usingrnmicroscopy or rapid diagnostic tests.We conclude thatrnoverdiagnosis may be prevalent in this district and there mayrnbe a need to design an intervention to minimise it.
Publication Information
Focus County(s):
Nyandarua County
Programme Area(s):
Infectious and Parasitic Diseases
Research Priority Area(s):
Disease Domain(s):
Document History:
Publication Date: 30.Apr.2019
Conference Title: