■多年来,疟疾的治疗是基于临床推定诊断,使其与其他原因的高热的鉴别诊断困难。这种药物压力导致疟原虫菌株对最常用的抗疟药具有抗性。这就是为什么在2004年,卫生当局决定修订疟疾管理政策,在对疑似疟疾病例进行生物学确认后,采用基于合理使用青蒿素联合疗法的新策略。生物诊断是疟疾管理的重要组成部分。诊断的金标准技术是厚滴结合寄生虫密度(PD)的计算,其基于在显微镜视野中计数的寄生虫的数量相对于所提出的白细胞的标准数量来确定。用于计算寄生虫密度的白细胞数量理想地应当是患者每立方毫米血液中白细胞的实际数量。然而,在厚滴时没有血细胞计数的情况下,世界卫生组织(WHO)使用平均8000白细胞/mm3来估计寄生虫密度。尽管如此,在贝宁,国家疟疾控制计划(PNLP)采用的白细胞平均数量为6000/mm3。我们研究的目的是确定在简单的疟疾病例中白细胞计数对寄生虫密度计算的影响。
■该研究是一项具有分析目的的横断面研究,在贝宁的两家医院进行,贝宁南部的Klouékanmey地区医院和北部的Djougou保健中心。它涉及476名年龄在6至59个月之间的儿童,他们在咨询中被发现,并且怀疑其临床诊断为单纯的恶性疟原虫疟疾。6至59个月的儿童,体重至少5公斤,包括咨询时腋窝温度≥37.5°C,或过去24小时有发热史,或有其他提示诊断为疟疾的症状.恶性疟原虫感染是单特异性的。需要得到孩子父母或监护人的知情同意。在我们的研究中,不纳入的标准是存在至少一种疟疾严重程度的迹象,与疟疾以外的潜在传染病有关的严重营养不良或发热状态的迹象。对所有纳入的儿童进行了系统的浓密血细胞计数和血象检查。根据3种方法计算寄生虫密度,首先使用贝宁国家疟疾控制计划(PNLP)建议的6000/mm3的加权白细胞计数,然后是世界卫生组织推荐的8000/mm3的白细胞计数,最后从血细胞计数中获得患者的实际白细胞计数。应当注意的是,这些不同的样品分别是在纳入当天按照我们的医学生物学实验室中有效的分析前阶段的条件采集的。
■在我们的研究结束时,313个孩子即65.76%的研究人群白细胞计数阳性,Djougou阳性率为62.14%,即174名儿童,而在Klouékanmey的70.9%,139个孩子这些儿童的平均白细胞计数为11,580/mm3。其中,205名儿童的白细胞计数异常,即白细胞减少17例(5.43%)和高白细胞增多188例(60.06%)。先后使用贝宁PNLP提出的6000个白细胞/mm3的平均数和WHO提出的8000个白细胞/mm3的平均数,当患者白细胞的真实数量用于计算PD时,平均寄生虫密度分别为47,943和63,936滋养体/μl,而32,290滋养体/μl。通过使用6000白细胞/mm3的平均值进行PD计算,60%的计算PD被低估,6%被高估。使用平均8000个白细胞/mm3导致49%的PD被低估,15%被高估。三种计算方法之间的差异被认为具有统计学意义(p值<0.05)。
■使用6000或8000系数来估计寄生虫血症可能会导致对寄生虫负荷的显着低估。
For many years, the treatment of malaria was based on clinical presumptive diagnosis, making its differential diagnosis with other causes of hyperthermia difficult. This drug pressure has led to the emergence of Plasmodium strains resistant to the most commonly used antimalarial drugs. This is why in 2004, the health authorities decided to revise the policy of malaria management by adopting a new strategy based on the rational use of artemisininbased combination therapies after the biological confirmation of suspected malaria cases. The biological diagnosis is an essential part of malaria management. The gold standard technique for diagnosis is the thick drop combined with the calculation of parasite density (PD), which is determined on the basis of the number of parasites counted in a microscopic field against a proposed standard number of leukocytes. The number of leukocytes used to calculate the parasite density should ideally be the actual number of leukocytes in the patient per cubic millimetre of blood. However, in the absence of the availability of a blood count at the time of the thick drop, an average number of 8 000 leukocytes/mm3 was used by the World Health Organisation (WHO) to estimate the parasite density. Nonetheless, in Benin the average number of leukocytes adopted by the National Malaria Control Programme (PNLP) is 6 000/mm3. The aim of our study was to determine the impact of the leukocyte count on the calculation of the parasite density in cases of uncomplicated malaria.
The study was a cross-sectional study with an analytical aim and took place in 2 hospitals in Benin, the Klouékanmey zone hospital in the south of Benin and the Djougou health centre in the north. It involved a population of 476 children aged between 6 and 59 months who were seen in consultation and in whom the clinical diagnosis of simple Plasmodium falciparum malaria was suspected. Children aged between 6 and 59 months, weighing at least 5 kg, with an axillary temperature ≥ 37.5°C at the time of consultation or a history of fever in the last 24 hours or other symptoms pointing to the diagnosis of malaria were included. Infestation was mono-specific for Plasmodium falciparum. Informed consent was required from the child\'s parents or guardian. The criteria for non-inclusion in our study were the presence of at least one sign of malaria severity, signs of severe malnutrition or a febrile state related to underlying infectious diseases other than malaria. Thick blood count and haemogram were systematically performed in all included children. Parasite density was calculated according to 3 methods, first using a weighted leukocyte count of 6 000/mm3 recommended by the Benin National Malaria Control Programme (PNLP), then a leukocyte count of 8 000/mm3 recommended by the World Health Organisation and finally the patient\'s actual leukocyte count obtained from the blood count. It should be noted that these different samples were respectively taken on the day of inclusion in compliance with the conditions of the pre-analytical phase in force in our medical biology laboratory.
At the end of our study, 313 children, i.e. 65.76% of our study population had a positive white blood cell count with a positivity rate of 62.14% in Djougou, i.e. 174 children, and 70.9% in Klouékanmey, i.e. 139 children. The average leukocyte count in these children was 11,580/mm3. Among them, 205 children had an abnormal white blood cell count, i.e. 17 cases of leukopenia (5.43%) and 188 cases of hyperleukocytosis (60.06%). Using successively the average number of 6 000 leukocytes/mm3 proposed by the Benin PNLP and that of 8 000 leukocytes/mm3 proposed by the WHO, the average parasite densities were respectively 47,943 and 63,936 trophozoïtes/µl against 92,290 trophozoïtes/µl when the real number of leukocytes of the patients was used for the calculation of the PD. By using an average of 6 000 leukocytes/mm3 for PD calculation, 60% of the calculated PDs were underestimated and 6% were overestimated. Using an average of 8 000 leukocytes/mm3 resulted in 49% of PD being underestimated and 15% being overestimated. The difference between the three calculation methods was considered statistically significant (p value <0.05).
The use of 6 000 or 8 000 coefficients for the estimation of parasitaemia could lead to a significant underestimation of the parasite load.