MALARIA INCIDENCE PATTERN: SPATIO-TEMPORAL ANALYSIS

Transcription

1 CHAPTER IV MALARIA INCIDENCE PATTERN: SPATIO-TEMPORAL ANALYSIS 4.1 Introduction Malaria epidemiological data pertaining to the district were collected from District Malaria Office (DMO), Tezpur, Sonitpur District for the period from 2002 to The primary data at district level are usually collected by Surveillance Workers of a health sub-centres. A sub-centre is formed to serve a minimum population of 5000, covering three to five villages based on their size. Further, three to five sub-centres are grouped together to form a section and similarly some sections are grouped together to form a Primary Health Centre (PHC). In Sonitpur district there are all total eight PHCs which comprise 288 numbers of sub-centres spread over the district. However, recently the concerned government has abolished the concept of section in order to ensure fast mobilisation of funds and essential medical items to the common people. During last few years, epidemiological data were stored section wise in DMO, but 2006 onwards the DMO and all PHCs have been advised by state health department to keep and update data sub-centre wise. So, the epidemiological data collected for the study are both section and sub-centre wise, which include population, blood slide examined, total malaria positive cases, annual parasitic index (API), annual blood examined rate (ABER), Plasmodium falciparum (Pf) 69

2 cases, Pf % and slide positivity rate (SPR) etc. These data have been later analysed thoroughly to reveal the malaria incidence pattern in the study area. It is important to mention and define some of the techniques used to examine the malaria epidemiological data collected for the study. Annual Parasitic Index (API) is total number of malaria cases in a year per 1000 population. It is generally used to indicate the load of parasite in a population. An area with more than 2 API is considered as risk area. It is also used by health authorities to determine the priority list for Indoor Residual Spray in affected areas. It is calculated as API = Total number of malaria cases in a year Total population X 1000 Annual Blood Examined Rate (ABER) is the percentage of total blood slides collected and examined in a year to total population. It describes the total efforts taken by the health authorities to tackle the menace of malaria. As per National Malaria Eradication Programme (NMEP) more than 10% of the total population in a malaria affected area should be covered for collecting and examining blood slides. An area with less than 10% of ABER is considered as poor surveillance area. ABER is calculated as ABER = Total blood slide examined in a year Total population X

3 Plasmodium falciparum (Pf) percentage is the total number of Pf cases to total malaria positive cases. Plasmodium falciparum which is considered as one of the dangerous parasite is taken as an index of malaria endemicity in an area. More than 30% of Pf is considered as a high risk area. It is calculated as Pf % = Total number of Pf cases Total number of slides positive for malaria X 100 Slide Positivity Rate (SPR) is the percent of total number of positive slides for malaria to total number of blood slide examined. It is also a vital tool to observe the endemicity of malaria in an area. It is calculated as SPR = Total number of slides positive for malaria Total number of blood slide examined X Distribution of health centres In order to find out spatial and temporal variation pattern of epidemiological cases of malaria, GIS has been applied. As many as 15 numbers of topological maps (1:50,000 scale) of the study area are acquired from the Survey of India which are further scanned and georeferenced to prepare base maps in GIS environment with the help of ESRI ArcMap TM 9.3 software. Base map of the study area has been prepared from the toposheets representing different layers like district boundary, rivers, water bodies, roads, villages (settlements) etc. 71

4 Figure 4.1: GPS location of health centres in Sonitpur district GPS survey has also been carried out with the help of handheld Garmin ique M5 GPS and Garmin Oregon 550 GPS to locate sub-centres, mini primary health centres, community health centres and hospitals of the study area so that the actual positions of the health centres could be mapped (Fig. 4.1). Later on the registered sub-centres and data in respect of them are put into ArcGIS software environment for advance mapping. A team consisting of surveillance workers, malaria inspectors, assistance malaria officer and district malaria officer has helped in delineating jurisdiction of each sub-centre located by GPS in the district. The team based on onscreen observation of village location and physical set-up both on toposheets and satellite imageries has demarcated all sub-centres within the district (Fig. 4.2). Epidemiological data from 2006 to 2010, as collected from DMO are later on attached to the jurisdiction data of each concerned sub-centre. Further, analysis has been done with the application of GIS in order to obtain better results. 72

5 Figure 4.2: Location of sub-centres in Sonitpur district 4.3 Spatial distribution of malaria incidence Spatial distribution of malaria incidence in the study area is based on epidemiological data of of the sub-centres. The spatial pattern of the incidences has been examined taking physiography, vegetation, prevalence of parasite and its trend into consideration. Attempt has been made to analyse the distribution of malaria incidence in respect of physiographic zone and vegetation zones Physiographic zone wise distribution Physiographically the district can be divided into two zones. One zone is the foothill region which is located along the northern boundary of the district and the other one is plain and flood zone located just south of the foothill region. The elevation of the district varies between 40 and 480 metres from the Mean Sea Level. There are some hillocks in the southern part, while the elevated plain surfaces lie adjacent to the foothills. The slope of the entire district trends from 73

6 north to south rising towards the foothills. In the north-central part, a strip of land with a height upto 300 metres is observed. The foothills can roughly be regarded as the boundary line separating the district (Assam) from Arunachal Pradesh. While considering the epidemiological data of malaria in the district since , it is found that the high number of cases were registered in the northern part of the district. The malaria cases above 200 are found between the height ranges from 60 to 300 metres with exception in one sub-centre (Fig. 4.3). This sub-centre registering positive cases above 200 is located between 41and 60 metres, which is due to the physical location of the Biswanath Charali civil hospital in the periphery of the sub-centre area. For getting better treatment in a civil hospital, people usually come and thus more cases are being registered in this sub-centre. Figure 4.3: Elevation wise malaria incidence pattern in Sonitpur district 74

7 The number of malaria cases get increased as the height increases towards the foothill region. The cause for the occurrence of malaria cases in a height between 60 and 300 metres is because of the existence of small slow flowing streams and rivers that come out from the foothill region, which are potential mosquito breeding sites. The Anopheles mosquito which is the vector responsible for malaria prefers to breed in slow flowing streams, which are commonly found in this area Vegetation zone wise distribution Looking into the vegetation types and pattern in the district, some dense forest patches as reserved forests are found located in the northern part of the district. These mainly include the Balipara reserved forest, Charduar reserved forest and Behali reserved forest. A total of around 686 km 2 of area comes under dense forest in the district as calculated using PCI Geomatica software. A large area under vegetation in the form of trees in tea gardens planted for shading purpose and local trees in and around villages comprises 1403 km 2. Figure 4.4: Vegetation areas and malaria incidence pattern in Sonitpur district 75

8 In view of the epidemiological conditions of malaria, it has been already mentioned that, the cases are registered in more numbers in the northern fringe of the district. The numbers of malaria cases are found to increase towards north as the forest areas are approached. Many sub-centres with registered cases more than 100 and 200 are situated in and around the forest area (Fig. 4.4). The forest areas are the good and ideal sites of mosquito breeding. Generally the mosquitoes breed in the foot marks of animals, tree hollow, small pool of water etc. Many of the vector species of Anopheles mosquitoes prefer to live in forest areas which happen to be their suitable habitat. The slow flowing streams and rivers in the forest areas provide suitable conditions for mosquito breeding. The presence of the parasite in the forest areas add oils into the fire, thereby enhancing spreading of malaria. The most important reason for malaria incidence is the encroachment of new settlers into the forest area. These settlers for their livelihood indulge themselves in forest and agricultural activities in the foothill region and thus they become easy target for malaria Malaria parasite prevalence pattern Malaria is a parasitic disease that is transmitted through biting of infected female Anopheles mosquito. This infected mosquito carries the parasite which is of four types. Out of these four types two types are dominant in the study area. They are Plasmodium falciparum and Plasmodium vivax. Among all malaria parasites, Plasmodium falciparum is the deadliest recording highest human deaths in the world. 76

9 Plasmodium falciparum parasite: The epidemiological situation of malaria along with the prevalence of Plasmodium falciparum in the district is observed. Since 2006, a total of (63.89%) number of Plasmodium falciparum affected cases out of a total of total malaria positive cases are being registered in different sub-centres of the district. The distribution of the Plasmodium falciparum cases shows that their occurrence is mostly confined to the northern part of the district. The number of sub-centres recording more than 200 cases of Plasmodium falciparum counts to 20 of which 5 sub-centres each are located under Dhekiajuli, Rangapara and North Jamuguri PHC, 2 each are under Biswanath Charali and Gohpur PHC and one is under Balipara PHC (Fig. 4.5). Number of cases ranging between 100 and 200 are reported from 21 sub-centres, followed by 29 sub-centres recording in the range between 50 and 100 cases in the district. Sonajuli sub-centre under Rangapara PHC has recorded a highest of 673 cases of Plasmodium falciparum during Figure 4.5: Distribution of Plasmodium falciparum cases in Sonitpur district 77

10 It can be stated that the Plasmodium falciparum spreads widely in the district. The western and north central parts of the district record high dominance of this parasite, while some isolated pockets are found in the eastern part of the district under Behali and Gohpur PHC s where this parasitic dominantly occur. Plasmodium vivax parasite: Normally Plasmodium vivax is less risky. But, its occurrence is high as revealed by the high number registered cases. A total of (36.11%) cases of Plasmodium vivax out of total cases of were recorded from different parts of the district since The concentration of Plasmodium vivax cases is more in the north central part of the district (Fig. 4.6). Some patches covering sub-centres with high incidence of this parasite are located in the western and eastern part of the district. Figure 4.6: Distribution of Plasmodium vivax cases in Sonitpur district The number of sub-centres with Plasmodium vivax cases more than 200 are found mostly under Balipara PHC with a total number of four followed by 78

11 three numbers of sub-centres in Biswanath Charali PHC and one sub-centre each in Rangapara and Dhekiajuli PHCs. The total number of sub-centers recording cases between 100 and 200 counts to 16 and in the range between 50 and 100 cases counts to 34. The highest numbers of Plasmodium vivax cases are being reported from Kadamani sub-centre under Biswanath Charlai PHC. Five numbers of sub-centres are such that they have recorded both falciparum and vivax with cases more than 200 each. These sub-centres are Tinisuti and Dhuli under Biswanath charali, Sonajuli, Amloga and Panbari chanimari under Rangapara, Balipara and Dhekiajuli PHCs respectively. 4.4 Trend of malaria incidence The general trend of malaria incidence reveals a decreasing trend in the study area. Since 2006 up to 2010 the number of sub-centres without a single case of malaria has increased from 72 to 177 which indicate a declining trend of malaria cases in the district (Fig. 4.7). The number of sub-centres with malaria cases above 50 per year has decreased from 46 in 2006 to 4 in During this period the number of cases in the district has greatly come down to 2622 from Such a declining trend of malaria incidence may be attributed to implementation of malaria control strategies like the use of rapid diagnostic kit, updated drug policy, indoor residual spray of DDT, impregnation of insecticide in mosquito bed nets and the supply of long lasting impregnated bed nets. 79

12 Figure 4.7: Changing pattern of malaria positive cases in Sonitpur district during Monthly and annual pattern In order to analyse the temporal pattern of malaria incidence in the district, related data have been taken for 20 years i.e. from 1991 to The temporal data of malaria incidence are taken monthly as well as annual basis. The monthly data are collected in respect of the four seasons in a year such as pre monsoon, monsoon, post monsoon and winter. Since 1994, there has been a decreasing trend in the number of cases. The number of cases has come down from a whopping high of in 1994 to 2622 in 2010 (Fig. 4.8). It records a ten times reduction of malaria cases in a period of 16 years. Although the trend shows a general decline of malaria cases, there are, however ups and downs over the years. Since 1991 the epidemiological data reveal that there were 5 instances when the number of malaria cases has increased from the preceding years. The sudden increase of malaria cases may be due to epidemic spread of the disease. Such epidemic incidences of malaria were recorded in the years of 1993, 1994, 1999, 2001 and 2006 (Fig. 4.8). But, while considering the 80

13 Malaria Cases (in numbers) MALARIA INCIDENCE PATTERN: SPATIO TEMPORAL ANALYSIS data for last 20 years, it has been found that there is an overall decrease in the number of malaria cases in the district. Since 2001 the epidemiological data suggest gradual reduction in malaria cases but a sudden rise in the number of cases was observed in 2005 and Since 2006 again a declining trend in the number of malaria cases has been observed MALARIA CASES IN SONITPUR DISTRICT ( ) Total Positive cases Years Source: District Malaria Office, Tezpur, Assam Figure 4.8: Yearly malaria cases in Sonitpur district While looking into the month wise malaria incidence over years since 1991, a pattern of irregular variation is observed. Every year since 1991 registered a slight or sometimes more increase of malaria cases during the rainy months from May to July. But, this rise fluctuates from year to year (Fig. 4.9). The data also reveal that two or more peaks of malaria incidences in a particular year also occur. 81

14 Jan Sep May Jan Sep May Jan Sep May Jan Sep May Jan Sep May Jan Sep May Jan Sep May Jan Sep May Jan Sep May Jan Sep May Malaria Cases (in numbers) MALARIA INCIDENCE PATTERN: SPATIO TEMPORAL ANALYSIS This type of variation can be noticed till 1997, especially in the years of 1992, 1993, 1994, 1996 and But, no such abnormalities have been observed in recent years. As mentioned earlier a gradual decrease of malaria cases was observed since However, a noticeable decrease in the number of malaria cases was noticed from 2006 till MALARIA CASES IN SONITPUR DISTRICT ( ) Total Positive cases Years Source: District Malaria Office, Tezpur, Assam Figure 4.9: Monthly variation of malaria cases in Sonitpur district during Periodic incidence pattern So far the periodic malaria incidence pattern is considered, the pre monsoon and monsoon months extending from March to August generally record high incidence of malaria. The summer months of May, June and July again record 82

15 Malaria Cases (in numbers) MALARIA INCIDENCE PATTERN: SPATIO TEMPORAL ANALYSIS highest malaria cases during the year (Fig. 4.10). The availability of water in streams, swamps and paddy fields during this period enhances proliferation of mosquito and as such these increase the load of disease in the period MONTHWISE MALARIA CASES ( ) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Winter Pre Monsoon Monsoon Post Monsoon Winter Source: District Malaria Office, Tezpur, Assam Figure 4.10: Seasonal variation of malaria cases in Sonitpur district during As malaria is water dominated disease, the cases of malaria always show a positive correlation with rainfall. The increase in frequency and amount of rainfall results in afterward increase in malaria cases. Once the agricultural lands and streams get filled with water, a time period of 15 to 20 days is needed for multiplication of mosquitoes and a 15 days time is needed for showing malaria symptoms in human. After biting by an infected female Anopheles mosquito, the parasite in human body stays for a two week time after which the first symptoms 83

16 for malaria indicate the presence of the disease. As the district receives rainfall before the actual monsoon arrives, the malaria incidence shows a peak in the month of June every year. Winter season: The winter season is the period when the number of cases of malaria in a region diminishes. The months in which winter season prevails in the study area are December, January and February. During this period the rainfall and temperature go on decreasing. The average maximum temperature during this period ranges from 23.8 C to 25.8 C and the average minimum temperature ranges from 11.4 C to 14.1 C. These maximum and minimum temperature conditions are not fairly suitable for the mosquito to grow. During this season, the average rainfall recorded since 1965 to 2010 ranges between 5.3 and 21.2 mm of rainfall, which too deter the outgrowth of mosquito. The number of malaria cases during the winter period is comparatively less than that in the other months of the year. The registered cases since 1991 were as low as 22 with a highest of 921 cases from December to February. The 921 number of cases were recorded earlier in December 1994 when there was an epidemic of malaria. The average number of cases of malaria since 1991 stored between 150 and 241 cases. As mentioned earlier the period from 1993 to1997 is a period of epidemic when the average number of cases had increased. While considering the data of last ten years, it has been found that the average malaria cases ranges between 52 to 86 from December to February. Pre monsoon season: The pre monsoon season in the study area comprises three months i.e. March, April and May. This is the period when a little amount of 84

17 rainfall is recorded after a long gap of four to five months. The dry land absorbs almost all of the rainfall water and a partial amount is left over for surface flow. But in the later part of the season, i.e. last part of April and whole of May, lands are found to be covered with water. This accumulation of water creates opportunities for mosquito to proliferate. The average rainfall since 1965 to 2010 recorded 48 to 241 mm of rainfall and the temperature, both average minimum and maximum, ranges between 17.8 C to 24.3 C and 29 C to 31.1 C respectively. The relative humidity also maintains a range between 60% to 75%. These temperature and humidity ranges are suitable for the mosquito growth. The number of cases get increased in this season compared to previous. The availability of mosquito and parasite produces ample scope for disease emergence. The cases since 1991 recorded during this season accounts highest of 6024 in May 1995 and a lowest of 42 in March The average number of malaria cases in 20 years recorded 230, 470 and 1440 in the months of March, April and May respectively. In last 10 years, the average malaria cases during this period has come down and being recorded as 133, 345 and 1178 from March to May. Monsoon season: During monsoon season this region in the subcontinent receives highest rainfall. Almost all days in the month of June, July and August recorded rainfall in this region. The water from rainfall as already being absorbed by the land is either locked in agricultural fields, ponds, ditches and lakes or overflows the excessive water over plains and creates flood. The average rainfall in Sonitpur district recorded 290 to 350 mm of water during this period. The average maximum and minimum temperature records 31.9 C to 32.7 C and 25.7 C to 85

18 26.7 C respectively and the relative humidity maintains a range between 80 % to 85 %. The number of malaria cases registered high as compared to pre monsoon period. The average number of cases in June, July and August recorded 1916, 1351 and 723 respectively since During last ten years the average malaria cases in the months from June to August indicates a gradual decrease and register 1697, 865 and 386 cases respectively. Post monsoon season: The post monsoon comprises three months from September to November when the rainfall decreases. In other words an arrest of rainfall that continues for almost six months. The average rainfall in the month of September recorded 205mm and 15mm in the month of November. The average temperature shows a minimum of 17.8 C to 25.9 C and a maximum of 27.9 C to 32.3 C where as the humidity ranges between 71% to 80%. The number of malaria cases during this season decreases. The average cases in the month of September, October and November during post monsoon season since 1991 was 569, 409 and 561 respectively. Looking into the last ten years average the cases have reduced to 232, 160 and 137 in the same months. The cause of the decrease in malaria cases is due to the decrease in mosquito population by heavy showers and washout of larvae due to flash flood during monsoon period. 4.5 Changing pattern and recent health policies The malaria situation in Sonitpur district since 1991 indicates how the pattern of cases have been changing month wise as well as year wise. The monthly 86

19 variation in malaria cases is because of the changing pattern in the climatic variables. The yearly variation though influenced by the climatic variables, but the recent implication of health policy by the government has changed the occurrence pattern of malaria monthly and yearly. In April 2005 in response to the acute deficiency of the primary health facilities in the country in providing basic health facilities to people living in rural areas National Rural Health Mission (NRHM) was launched in India. The basic aim was to provide better health service to poorest and disadvantaged people living in rural areas. Village community participation was involved for decision making process and achieving health goals. A good number of arrays were used in the country as well in Assam for development of health infrastructure like Human resource development by recruiting Doctors, Specialists, Nurses, Auxiliary Nurse and Mid-Wife (ANMs), Accredited Social Health Activists (ASHAs), Paramedical staff etc., physical up gradation of infrastructure like sub-centres, PHCs, CHCs, sub district and district hospitals, introduction of Mobile Medical Units, Ambulances and Emergency Transport like 108 &104, different schemes like Janani suraksha, Mamoni, Majoni etc. and strong rules and regulations for staff like compulsory rural posting of Doctors in rural areas etc. Apart from these the use of Rapid Detection Kits (RDK), Insecticide Treated Bed nets (ITNs), free Govt. distribution of Long Lasting Insecticidal Nets (LLINs), DDT spray in houses, use of new drug etc. helped in curving the success story in Assam. The recent change in the drug policy for malaria contributed in reduction of malaria cases. Artemisinin Combination Therapy (ACT) for the treatment of Pf 87

20 cases is successful in the high risk malaria prone areas. The use of mass communication through different means assisted in the popularizing and creating awareness among people. Popular talks on malaria were aired through Radio and Television. Radio jingles by AIR and FM, awareness clips on malaria were telecasted in channels of television, news paper insertion, hording & wall painting and rally were used. These efforts gave fruitful results as the epidemiological data of malaria suggest the decrease in the diseases pattern of malaria in Assam and Sonitpur district too ascertains the report. 88