Impact of a double dose of sulphadoxine–pyrimethamine to reduce prevalence of pregnancy malaria in southern Mozambique

Authors


Authors
Kenneth Challis (corresponding author) and Gunnar Nordahl, Sundsvall Hospital, 85186 Sundsvall, Sweden. E-mail: kenneth.challis@lvn.se,gunnar.nordahl@alfa.telenordia.se
Nafissa Bique Osman and Manuel Cotiro, Department of Obstetrics and Gynaecology, Central Hospital, Maputo, Mozambique. E-mail: osman@mail.tropical.co.mz,cotiro@trcabo.co.mz
Martinho Dgedge, Instituto Nacional de Saúde, Ministry of Health, Maputo, Mozambique. E-mail: uffo@zebra.uem.mz
Staffan Bergström, Division of International Health (IHCAR), Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden. E-mail: staffan.bergstrom@phs.ki.se

Summary

Malarial infection during pregnancy increases the risks of severe sequelae for the pregnant woman and the risk of delivering a low birthweight baby. The aim of this intervention study was to reduce significantly the prevalence of malaria parasitaemia in adolescent parturients in Matola and Boane in Mozambique. The study was focused upon the most malaria-vulnerable group, adolescent nulliparous and primiparous women. After completing the usual antenatal clinic and giving informed consent, 600 pregnant women were randomly chosen in a double blind manner to one of two regimens comparing the prevailing routine (placebo) for malaria prevention with a two dose regimen of sulphadoxine–pyrimethamine (SP). The first dose was given at enrolment with a second dose at the beginning of the third trimester. At delivery maternal and placental malaria parasitaemia as well as birthweight and gestational duration were analysed. At booking the prevalence of malaria parasitaemia was 35.3% in the placebo group and 30.6% in the SP group. At the second dose, the prevalence of malaria parasitaemia in the placebo group and SP group was 19.7% and 8.7%, respectively. This implies a relative risk (RR) of 2.24 with 95% CI (1.34, 3.75). The corresponding figures at delivery were 13.6% and 6.3% with an RR of 2.22 (1.07, 4.60) and in placenta 13.3% and 2.4% with an RR of 4.87 (1.58, 15.0). Newborns with malaria within 7 days were significantly more frequent in the placebo group, 6.4% and 0.7% respectively, with an RR of 6.55 (1.20, 35.7). Almost all (approximately 98%) of the women studied had Plasmodium falciparum, the remainder had P. malariae and P. ovale. The mean birthweight in the SP group was 3077 g and in the placebo group 2926 g. The estimated mean difference between the two groups was 151 g with 95% CI (51, 252). The mean placental weight in the placebo group was 596 and 645 g in the SP group, implying a difference of 49 g with a 95% CI (11, 88). The mean gestational duration was 6.1 days longer in the SP group, 95% CI (1.5, 10.6). In the placebo group there were two cases of urticaria and one case of nausea; in the SP group there was one case of vomiting. No newborn showed any sign of serious SP side-effect. Two doses of SP were enough to significantly reduce the prevalence of peripheral and placental malaria parasitaemia among young nulliparous and primiparous pregnant women in Matola and Boane.

Introduction

According to statistics from WHO malaria is the largest parasitic disease killer globally. Malaria kills two persons every minute. Globally, malaria causes 1–3 million deaths per year and 90% of these occur in Sub-Saharan Africa. Children and pregnant women are the most affected with malaria (WHO 1990, 1998).

Malaria infection during pregnancy increases the risks of severe sequelae for the pregnant woman and the risk of delivering a low birthweight (LBW) baby (Steketee et al. 2001). Approximately 95% of all LBW newborns (<2500 g), in the world occur in low-income countries. Adverse environmental circumstances, particularly food deficiency is also associated with LBW (Andersson & Bergstrom 1997; Ngare & Neumann 1998; Ogunyemi et al. 1998). We know from earlier studies in Mozambique (Bique Osman et al. 1993, 1995; Axemo 1995) and other low-income countries (Sullivan et al. 1999) that besides socio-economic factors, adverse perinatal outcome is strongly correlated with infections such as malaria, syphilis and anaerobic intrauterine infections. The rates of perinatal morbidity and mortality are high in Mozambique (Liljestrand et al. 1992; Axemo 1995). Infant mortality among LBW babies is four times that of normal birthweight babies (Osman et al. 2001). The prevalence of malaria in pregnant women is high; the most common (>90%) parasite is Plasmodium falciparum (Saute et al. 2002). Lately the number of cases of lethal cerebral malaria among young nullipara and primipara has increased considerably in Maputo City and province (F. Machungo, unpublished data). Interventions to reduce maternal and perinatal infant mortality and morbidity should focus upon early detection and management of recognizable factors affecting maternal health. Antenatal screening is an important tool.

Malaria transmission (P. falciparum, 90%) in Mozambique is perennial with a peak season from February to May. Chloroquine (CQ) resistance is at 30–50% in Mozambique and surrounding countries (Schwalbach et al. 1985; Schapira & Da Costa 1988; Bloland et al. 1993; Schultz et al. 1994; Steketee et al. 1996c; Mayor et al. 2001). In 1992, the Ministry of Health dropped CQ prophylaxis. Currently, first-line regimen is CQ, the second-line regimen sulphadoxine–pyrimethamine (SP), and the third quinine solution intravenously (Schapira 1988).

Studies in Kenya (Steketee et al. 1987; Parise et al. 1998) and Malawi (Steketee et al. 1996d) established that one feasible way of handling the huge malaria morbidity is to target high-risk pregnancies (Steketee et al. 1996b). Young pregnant women face a double risk (Brabin 1983; McGregor 1984). Their immune system against the malaria parasites is not complete until the age of 20 (Smith et al. 1994), and pregnancy in itself weakens the immune system (Sholapurkar et al. 1990). However, most studies have shown that the bigger risk factor for malaria parasitaemia during pregnancy is parity (Steketee et al. 1996b,d). Giving SP as a treatment dose at the first antenatal clinic visit and at the beginning of the third trimester is highly effective in reducing peripheral and placental malaria parasitaemia (Schultz et al. 1994; Verhoeff et al. 1998). With this treatment there were few and now serious side-effects and it was cost-effective in preventing placental malaria and LBW-associated mortality (Schultz et al. 1996). No studies have been carried out in Mozambique regarding P. falciparum being resistant to SP. Such resistance has been demonstrated in other countries (Bredenkamp et al. 2001; Omar et al. 2001; Blair-Trujillo et al. 2002; Hayton et al. 2002).

The purpose of this study in southern Mozambique was to examine whether the prevalence of adolescent parturients with malaria parasitaemia could be reduced significantly by using SP.

Subjects and methods

The study population was 600 nulliparous and primiparous women in Matola and Boane under 21 years of age. Data from our cohort study indicate that the prevalence of malaria parasitaemia in the maternity 1° Maio area (suburban area of Maputo) was low (4%) in comparison with Mozambique in general (10–40%) (WHO 1998). Afterwards we were informed that the Ministry of Health had sprayed this area with insecticide. This time we were recommended, by the Instituto Nacional de Saùde to go to Matola, a town just outside Maputo, which had never been sprayed with insecticides. Boane, a village 40 km from Maputo, was also recommended. From the pilot study in Matola 1998/9 we learnt that we needed to minimize the drop out rate, which was disturbingly high (about 70%).

The Ministry of Health informed us that among pregnant women the HIV prevalence in the areas at the time was about 10% and malaria prevalence about 20%. Considering an intended reduction of parasitaemia prevalence by 50% placebo vs. SP with 80% power and a significance level of 0.05 we calculated a need of 220 participants in each group. With an estimated drop-out rate of 25%, we decided to have two groups each consisting of 300 pregnant women. This study was conducted from January 2001 to July 2002.

Enrolment

Only the most malaria-vulnerable groups (nulliparous and primiparous below 21 years of age) were enrolled. Women living in houses that had been sprayed with insecticide were excluded. Women who did not intend to continue the antenatal care and/or deliver at the hospital in Boane or Matola were excluded. We also excluded women with gestational age >28 weeks as they were regarded to be too late for two doses. We avoided giving SP before 15 weeks of gestations for safety reasons and those women had to come back later or be excluded.

The enrolment procedure and the antenatal care and delivery care were performed by midwives trained for the project and supervised by members of the research group. The usual antenatal clinical examination was completed by a questionnaire to collect information on illness or treatment during current pregnancy, allergy, education and other socio-economic factors (type of house, water supply, latrine, electricity and family size). Within the antenatal routine a capillary blood sample was drawn for a malaria thick blood smear. Venous blood was drawn for estimating haemoglobin photometrically by using a haemoglobinometer (Biotron, Biotron Ltd, Sydney, Australia). After completing the usual antenatal clinic and proving informed consent, the women who gave their consent (signed with their name or thumbprint) were randomly assigned to one of two regimens and packages of three tablets (SP or placebo) were given in a double-blind manner: either SP/SP – an initial treatment dose of SP at enrolment with a second dose at the beginning of the third trimester; or placebo/placebo – an initial dose at enrolment and a second dose of placebo at the beginning of the third trimester.

The SP dose was 1500 mg of sulfadoxine and 75 mg of pyrimethamine given as a single dose of three tablets. All tablets were taken by the women at the antenatal clinic at the hospital and supervised by the trained midwife. The placebo dose was three similar tablets in shape and colour as SP tablets but with glucose instead of SP.

Follow-up

During the usual monthly antenatal care, the enrolled women were asked to provide information on interim history of fever and side-effects attributable to the medicine. At the beginning of the third trimester a second dose of SP or placebo was given. At the same time a capillary blood sample was drawn for a malaria thick blood smear. Any woman with clinical symptoms of malaria was treated, irrespective of allotment in the trial. The treatment followed the guidelines issued by the Ministry of Health: option 1: CQ; option 2: SP; option 3: quinine and tetracycline (Schapira 1988).

Delivery

All women were recommended delivery in the Maternity in Matola II, the Boane Maternity or in emergency situations in Jose Macamo Hospital or the Central Hospital in Maputo. At delivery a questionnaire was administered and a capillary blood sample was collected for malaria thick smear examination. Birthweight (within 24 h) and gestational age (determined by using menstrual data) were registered. The placenta was weighed, and a sample was collected from the maternal side of the placenta for thick smears. All malaria slides were coloured with Giemsa. A smear was considered to be negative only if no parasites were detected after a minimum of 500 leucocytes had been counted. All slides were analysed and double checked at the special malaria laboratory at the Ministry of Health. Those women who did not comply with the required institutional delivery, or failed to attend with their babies after the estimated date of delivery were visited at home.

Statistical methods

The data were analysed on an intention-to-treat (ITT) basis. ITT includes a random allocation procedure producing comparable groups and an analysis of the data according to the way we intended to treat the subjects. The ITT analysis is defined in the context of a randomized clinical trial (RCT).

When comparing the outcomes in the placebo group and SP group, relative risk (RR) was used for the dichotomous variables and absolute difference for the quantitative variables. The quantitative variable gestational duration was also analysed, using the Mann–Whitney test, after a split into four different pregnancy outcomes, late spontaneous abortion [≤27 weeks (w) + 6 days (d)], pre-term (28 w + 0 d) to (36 w + 6 d), term (37 w + 0 d) to (41 w + 6 d) and post-term (≥42 w + 0 d) birth.

Data were registered using Epi-info 6.02 (Center for Disease Control and Prevention, Atlanta, GA, USA). The statistical analysis utilized SPSS for windows version 10.1 (SPSS Inc., Chicago, IL, USA). When calculating RR and the corresponding confidence intervals, a less biased estimator than the ordinary sample RR was used. The RR-algorithm was implemented in Mathematica for windows version 4.2 (Wolfram Research, Inc.). Confidence intervals for differences were calculated using ordinary t intervals, assuming approximately the same variance in the two groups.

Ethical considerations

All nulliparous or primiparous pregnant women under 21 years, who were approached for enrolment were informed about the objectives of the study and that the normal antenatal care programme would be followed, except for the drug administration and blood samples. Participation was voluntary, and if they agreed to participate in the study they had to confirm acceptance by signing a form with their name or thumbprint. During the antenatal care the midwives were informed that they should ask and look for side-effects. The ethical committees of Karolinska Institutet, Sweden and Instituto Nacional de Saùde, Mozambique approved the project.

Results

Study population

The characteristics of the subjects at enrolment are shown in Table 1. In the study 600 women (300 placebo and 300 SP) were enrolled. There was 100% consent to the study but 33 women refused a blood test after enrolment. None were living in houses that had been sprayed with insecticide. At booking the prevalence of malaria parasitaemia was 35.3% in the placebo group and 30.6% in the SP group. Of the enrolled women 347 delivered at the Boane or Matola maternities and 56 at home or at other maternities. The newborns were weighed within 24 h.

Table 1.  Characteristics at enrolment of woman receiving placebo or sulphadoxine–pyrimethamine (SP) for malaria prevention in pregnancy in Boane and Matola, Mozambique, 2001–2002
CharacteristicPlacebo group (n = 300)SP group (n = 300)
Non-missing observations, n (%)Mean (SD) or relative frequency (%)Non-missing observations, n (%)Mean (SD) or relative frequency (%)
  1. * Low socio-economic status is defined as fulfilling at least one of the two characteristics: (i) living in house without electricity, and (ii) living in straw house or house made of cement blocks.

Age266 (88.7)18.5 (1.6)260 (86.7)18.6 (1.7)
No. years in school251 (83.7)5.4 (2.0)249 (83.0)5.2 (2.2)
Haemoglobin (g/dl)292 (97.3)11.4 (1.2)291 (97.0)11.5 (1.3)
0 parity260 (86.7)77.3262 (87.3)74.0
Low socio-economic status*271 (90.3)74.5265 (88.3)69.4
Maternal peripheral parasitaemia283 (94.3)35.3284 (94.7)30.6

At second dose, 411 women were available for a peripheral malaria smear and at delivery, 291 women. Thus, 309 women (153 women from the placebo group and 156 women from the SP group) were lost to the follow-up peripheral blood analyses at delivery because of logistical obstacles such as transport problems, emigration out of the study area or failure to return for follow-up, or when the study team was unable to locate their houses. We believe there were also psychological and other unidentified logistical reasons behind the drop outs. Only 203 placentas were weighed, but 244 were analysed for malaria. In the placebo group, 273 subjects (91.0%) complied with the treatment and took the three tablets both at enrolment and at the beginning of the third semester. The corresponding figure in the SP group was 272 (90.7%).

Impact of the SP regimen on malaria parasite prevalence

At the time of the second dose, the prevalence of malaria parasitaemia in the placebo and SP groups was 19.7% and 8.7%, respectively (Table 2). This implies an RR of 2.24 (1.34, 3.75). The corresponding figures at delivery were 2.22 (1.07, 4.60) and 4.87 (1.58–15.0) in the placenta (Table 2). Self-reported fever at least once during pregnancy showed eight cases with fever (of 86) in the placebo group and only two cases (of 88) in the SP group. Of those with fever in the placebo group three cases had fever several times, none in the SP group did. All cases with fever were analysed and treated for malaria. The RR of fever at least once during pregnancy in the placebo group was 3.48 (0.88–13.8) (Table 2).

Table 2.  Malaria parasite prevalence and delivery outcome in the placebo group and sulfadoxine–pyrimethamine (SP) group
Characteristic Dichotomous variablesPlacebo group (n = 300)SP group (n = 300)Comparison
n / No. non-missing observationsRelative frequency (%)n / No. non-missing observationsRelative frequency (%)Estimated RR95% CI for RR
Maternal peripheral parasitaemia at second dose40/20319.718/2088.72.24(1.34, 3.75)
Maternal peripheral parasitaemia at delivery21/14713.69/1446.32.22(1.07, 4.60)
Placental malaria16/12013.33/1242.44.87(1.58, 15.0)
LBW (<2500 g)27/20313.319/2009.51.39(0.80, 2.40)
Fever (self-reported) during pregnancy8/869.32/882.33.48(0.88, 13.8)
Pre-term delivery (<37 weeks)52/22423.240/21818.31.26(0.88, 1.82)
Spontaneous late abortion5/2242.20/2180.010.71(0.60, 192)
Newborn with malaria within 7 days10/1566.41/1460.76.55(1.20, 35.7)
Neonatal unit care14/1957.26/1953.12.23(0.90, 5.51)
Quantitative variablesNo. non-missing observationsMean (SD)No. non-missing observationsMean (SD)Estimated difference (SP-placebo)95% CI for difference
Birthweight (g)2032926 (494)2003077 (533)151(51, 252)
Weight of placenta (g)98 596 (127)105 645 (151)49.5(10.8, 88)
Length of pregnancy (days)224 269 (25.4)218 275 (22.7)6.1(1.5, 10.6)

Newborns with malaria within 7 days were significantly more frequent in the placebo group, RR = 6.55 (1.20, 35.7) (Table 2). Approximately 98% of women with malaria had P. falciparum, the rest had P. malariae and P. ovale infections.

The impact of the SP regimen on newborns

The mean birthweight in the SP group was 3077 g and in the placebo groups 2926 g (Table 2). The estimated mean difference between the mean values of the two groups was 166 g with 95% CI (51, 252). The mean placental weight in the placebo group was 596 and 645 g in the SP group, implying a difference of 49 g with 95% CI (11, 88). The mean length of pregnancy was 6.1 days longer in the SP group, 95% CI (1.5, 10.6). In Table 3 the length of pregnancy is classified into four groups. Also with this classification, the difference between the two groups is statistically significant. As can be seen in Table 2, none of the other of the investigated variables differed significantly.

Table 3.  Pregnancy outcome split into four classes. The difference between the placebo group and SP group is statistically significant (P = 0.024)
Pregnancy outcomePlacebo group (n = 300, non-missing observations = 224)SP group (n = 300, non-missing observations = 218)
nRelative frequency (%) nRelative frequency (%)
Spontaneous late abortion (≤27 w + 6 d)52.200.0
Pre-term (28 w + 0 d) to (36 w + 6 d)4721.04018.3
Term (37 w + 0 d) to (41 w + 6 d)15368.314466.1
Post-term (≥42 w + 0 d)198.53415.6

Side-effects for mother and child

In the placebo group there were two cases of urticaria and one case of nausea. In the SP group there was one case with vomiting. No newborn showed any sign of serious SP side-effects.

Discussion

The main result in our study was that, by using two doses of SP, among adolescent parturient women in Matola and Boane area prevalence of peripheral malaria parasitaemia was reduced significantly. The reduction was analysed both at the beginning of the third trimester and at delivery. Together with the result that placental malaria parasitaemia was lower in the SP group we could assume that the placenta had remained aparasitaemic for a longer period in the SP group (Bjorkman & Willcox 1986; Heymann et al. 1990), allowing for normal placental function and foetal growth. As a consequence of this reduction of placental malaria parasitaemia, the mean birthweight was significantly higher and the length of pregnancy significantly longer in the SP group.

At the second dose at the beginning of the third trimester the RR of peripheral malaria parasitaemia in the placebo group was double the one in the SP group. At delivery the RR of peripheral malaria parasitaemia was still double and in the placenta almost five times the one in the SP group. These elevated risks demonstrate the impact of SP on clearing peripheral and placental malaria parasitaemia. These results in SP clearing peripheral malaria parasitaemia are consistent with other recent studies in the region (Schultz et al. 1994; Parise et al. 1998).

Even in the placebo group there was a reduction of malaria parasitaemia at the second dose, at delivery and in the placenta. The explanation is probably the natural history of the immune response, which peaks in the third trimester (Brabin & Perrin 1985). Another explanation might be the circumstance that malaria symptomatic cases in the placebo group were treated in accordance with study design. The treatment given was CQ (or SP if CQ was insufficient) in accordance with guidelines from the Ministry of Health.

An arbitrary estimate of the proportion of treated malaria cases in the two groups was given by the self-reported fever. Four times more fever was reported in the placebo group – but the reported numbers were low (n = 154). It might be argued that this proportion of more treated malaria cases in the placebo group contributed to reduce the difference in the two groups regarding LBW prevalence.

The 10 women who reported fever were all slide confirmed, malaria – which is the routine at the antenatal clinics and health stations. However, the research team did not have the resources to check all the suspected malaria cases because of logistical problems. It is very hard to capture all malaria cases in an African countryside settlement of pregnant women. All women in the study were asked to attend our antenatal clinic or an associated health station in case of fever. However, some participants travelled on business or did not return for other reasons, there were transport problems, the laboratories did not work, or the women were treated at other health centres out of our control. We believe these problems occurred at random in the two groups.

The study was conducted during two rainy seasons and one dry season (18 months), which could explain the higher prevalence of malaria parasitaemia than expected on an annual basis. However there was no differential enrolment between placebo and SP group during the seasons. A forthcoming study of pregnant women in southern Mozambique (K. Challis, N. B. Osman, M. Cotiro, S. Bergström, unpublished data) shows that last menstrual period data frequently overestimate gestational length by about 1 week in comparison with ultrasound-dated gestational age. This might explain the high proportion of ‘post-term’ deliveries in the study. The mean length of pregnancy was about 1 week longer in the SP group – which is of significant importance.

At the end of the study there was the same rate of dropouts as in other recent similar malaria studies in southern Africa (Schultz et al. 1994; Parise et al. 1998; Verhoeff et al. 1998) despite our method to avoid loss by following up with incentives and our efforts to find them in their homes. The extent to which data from the lost women differ from the data of those retrieved is difficult to establish. Looking at socio-economic status, parity, etc. (Table 1), it appears that the characteristics of the drop out group are similar to those of the remaining group. The number of missing cases in the SP and placebo groups was also similar. In summary, it is unlikely that the failure to follow-up has altered the study results.

The mean haemoglobin value (11.4 g/dl) at enrolment is similar to the value of our cohort study in the suburban area of Maputo (Bique Osman et al. 2000). It is surprisingly good and evidently not affected by the high prevalence of malaria or the low socio-economic status, about 65% living in simple houses without electricity.

Plasmodium falciparum resistance to CQ is of great concern (Bloland et al. 1993). In order to avoid the same resistance development as for CQ in southern Africa, the intervention was to preemptively treat the most vulnerable group instead of disseminating malaria pre-emptive treatment to all pregnant women. By giving only adolescent nulliparous and primiparous women two doses of SP, we believe it might be possible to delay the development of P. falciparum resistance to SP. Molecular markers for resistance to SP have been identified (Kublin et al. 2002). We did not monitor the resistance molecularly but focused on the outcome of the treatment. The results indicate that parasite resistance to SP is not yet a significant problem.

Another great concern is HIV, which is increasing in the region (Bloland et al. 1995; Verhoeff et al. 1999c). Studies suggest that HIV infection may diminish a pregnant woman's capacity to control P. falciparum infection (Steketee et al. 1996a) and thus may lead to the decreased effectiveness of antimalarial drugs. Placental malaria parasitaemia in HIV-positive women may also increase the risk of vertical transmission of HIV (Bloland et al. 1995). We did not analyse HIV status in our study because there are insufficient resources for HIV testing in antenatal care in the country. We did not incorporate such testing in our study because it was not the standard of care and the Ministry of Health did not recommend such testing. In forthcoming studies on antimalarials to pregnant women, normally subject to antenatal HIV screening, this aspect will receive attention.

In areas with high prevalence of HIV (>12%) and high malaria transmission (>30%) several studies indicate a need for three doses or monthly SP treatment and not only to nulliparous and primiparous but to all pregnant women (Parise et al. 1998; Verhoeff et al. 1998, 1999a,b,c; Wolfe et al. 2001). In conclusion, in the setting studied, two doses of SP were enough to reduce peripheral and placental parasitaemia significantly. Our study also showed that the SP/SP package had a positive significant impact on the mean values of the birthweight, placenta weight and length of pregnancy. However, there is an urgent need for alternative, cost-effective, antimalarial regimen studies among pregnant women in order to ‘roll back malaria’ as SP efficacy may decrease over time, even in this semi-immune adult population of pregnant women. HIV prevalence is increasing and has been suggested to further compromise drug efficacy during pregnancy (Parise et al. 1998).

Acknowledgements

The study was made possible by grants from the Department of Research Co-operation with Developing countries (SAREC) at the Swedish International Development Authority (Sida) and from Mid Sweden Research and Development Centre (FoU). We acknowledge the valuable contribution to this field study by assistant medical officer Paulino Alfaia Cassucera and medical student Manuel Cotiro.

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