Effect of routine zinc supplementation on pneumonia in children aged 6 months to 3 years: randomised controlled trial in an urban slum

Study setting

The trial took place in the urban slum of Dakshinpuri in New Delhi, India, comprising 15 000 dwellings and 75 000 inhabitants. Recent data from a neighbouring community indicated that childhood malnutrition, zinc deficiency, diarrhoea, and lower respiratory tract infections were common. 3 11 12

Randomisation and masking

We included children if their parents gave informed consent. Eligible children were individually randomised by a simple randomisation scheme in blocks of eight. The randomisation scheme was generated by a statistician at Statens Serum Institut, not otherwise involved with this study, using SAS software. Zinc or placebo syrups were prepared and packaged in unbreakable bottles by GK Pharma ApS, Koge, Denmark, who also labelled bottles with a unique child identification number according to the randomisation scheme. Six bottles, one for each month and two extra, for each child were produced and labelled before enrolment commenced. The supplies for each child were kept separately in labelled plastic bags. The zinc and placebo syrups were similar in appearance, taste, and packaging. Masking was maintained during analyses by coding the groups as A or B.

Enrolment and intervention delivery

Enrolment commenced on 15 February 1999. All children aged 6 to 30 months in the community were identified through a survey. We excluded children if consent was refused, if they were likely to move out of the study area within the next four months, and if they needed urgent admission to hospital on the enrolment day or had received massive dose of vitamin A (100 000 IU for infants and 200 000 for older children) within the two months before enrolment. The follow up of the last child was completed on 30 September 2000.

Doses of elemental zinc were 10 mg for infants and 20 mg for children (twice the recommended daily doses) as zinc gluconate. Zinc or placebo was taken daily for four months. An attendant administered the syrup daily for four months except on Sundays, when the mother administered it. One bottle containing 250 ml was kept in the child's home and replaced monthly. Immunisations and treatment for acute illnesses were provided as per World Health Organization guidelines.13 Children with acute lower respiratory tract infections received co-trimoxazole. Amoxicillin was substituted if the child did not respond within three days. Children were sent to hospital if they had signs and symptoms that warranted referral according to WHO guidelines.13

We used Seca Salter scales and locally manufactured length boards that read to the nearest 0.1 kg and 0.1 cm respectively to assess growth at enrolment. The study was approved by the All India Institute of Medical Sciences ethics committee. Informed written consent was obtained from community leaders and parents. Signatures or thumb impressions were obtained on consent forms and a copy left with the family.

Measurement of outcomes

Field workers visited each child every seventh day during the entire study. At each visit, mothers were asked about fever, cough, other characteristics of illness, and whether they had sought treatment for the child in the previous seven days. Respiratory rates were counted twice for one minute each and the temperature recorded. Children with cough and respiratory rates ≥35/min at age ≥12 months and ≥45/min at <12 months or lower chest indrawing were brought to study physicians for assessment. We used the cut offs of 5 breaths/min below the WHO criteria for fast breathing to maximise detection of acute lower respiratory tract infections and pneumonia. Two study physicians examined and repeated measurements of respiratory rate, clinical indicators of hypoxaemia, and auscultation. In cases of disagreement, a senior paediatrician assessed the child. Mothers were encouraged to bring their children to the study clinic whenever they were ill and they were similarly assessed.

Acute lower respiratory tract infections were defined by cough and fast breathing or lower chest indrawing as assessed by the physician; other clinical signs were not taken into account.13 Fast breathing was defined as two counts of ≥50 breaths/min for infants and ≥40 breaths/min for older children. The day of onset of infection was the first day when this combination was detected. The day of recovery was the day after the last day when this combination was present. Pneumonia was diagnosed either by a combination of cough with crepitations or bronchial breathing by auscultation or as an episode of acute lower respiratory tract infection associated with at least one of lower chest indrawing, convulsions, not able to drink or feed, extreme lethargy, restlessness or irritability, nasal flaring, or abnormal sleepiness. For episodes to be counted as individual, there had to be at least 14 intervening days.

Sample size

We calculated sample sizes for 80% power with 95% level of confidence. We took values for the control group from a previous study in an adjacent slum, which reported 0.41 episodes of acute lower respiratory tract infection and 0.12 episodes of severe acute lower respiratory tract infections or pneumonia per child per four months.12 We required 907 children per group to detect a 20% or greater reduction in incidence of acute lower respiratory tract infections. We required a larger sample size of 1234 per group to detect a 30% or greater reduction in incidence of pneumonia.

Plasma zinc

At enrolment and at the end of the study we collected samples of non-fasting venous blood (about 5 ml) in zinc-free heparinised polypropylene tubes (Sarstedt, Nümbrecht, Germany) between 9 am and 12 noon. The samples were centrifuged and plasma transferred to zinc-free polypropylene vials (Eppendorf, Hinz, Germany) for storage at −20°C. About half of the plasma samples were analysed for zinc by a standard flame furnace atomic absorption spectrophotometer technique (GBC Avanta, Dandenong, Victoria, Australia) and the other half by inductively coupled plasma atomic emission spectrometry (Ash IRIS/AP, Thermo Jarell, MA, USA) using SERONORM (Sero AS, Billingstad, Norway) as the reference standard in every batch of 20 samples in both methods. The two methods were calibrated to give the same results before we started to analyses study samples. 14 15

Standardisation and quality control

We used a study manual describing standard operating procedures. Standardisation exercises were done to achieve agreement within and between study personnel for measurement of respiratory rate and anthropometry every three months. All physicians had some experience in paediatrics and were retrained in the recognition of crepitations, bronchial breathing, and wheezing by a senior paediatrician every three months.

Supervisors monitored field workers' activities. Independent supervisory checks to inquire about daily dispensing of the syrup (0.5% of total visits) and to authenticate the data collected at morbidity visits (1% of total visits) were made. Field workers were additionally observed at home visits (1% of visits) to assess counting of respiratory rate, measurement of temperature, and assessment of lower chest indrawing.

Data management and analysis

The forms for the study were designed with FoxPro for Windows (Microsoft Corporation, Redmond, Washington, USA) and range and consistency checks incorporated. Double data entry by two data clerks followed by validation was completed within 48 hours. We compared incidence of acute lower respiratory tract infections or pneumonia in the two groups and calculated absolute risk reductions with their 95% confidence intervals.16 For the person time analyses, the denominator was the days for which reliable information about illness was available.

To account for the correlation of multiple episodes in the same child, we used generalised estimating equations for longitudinal data analysis. The surveillance data for each child were divided into eight child periods of 15 days each. To be included in this analysis a child had to contribute at least 15 days of follow up to the denominator. In the generalised estimating equations model, occurrence of a new episode of acute lower respiratory tract infection or pneumonia in a child period was modelled as a binomial dependent variable and group allocation (zinc or placebo) as the independent variable. The model used a logit link, binomial variance, and exchangeable correlation.

Statistical analysis was performed with Stata, version 6 (StataCorp, College Station, TX).

Intervention efficacy

The mean plasma zinc concentration was significantly higher at the end of the study in the children who received zinc supplementation (19.8 (SD 10.1) v 9.3 (SD 2.1) μmol/l, P<0.001 non-parametric test). The change from enrolment was also substantially higher in the zinc group (10.4 (SD 10.0) μmol/l) compared with the placebo group (−0.3 (SD 2.2) μmol/l, P<0.0001 non-parametric test).

Acute lower respiratory tract infections

In the child based analyses, 425 children in the zinc group and 423 in the placebo group experienced at least one episode of acute lower respiratory tract infection (absolute risk reduction −0.2%, 95% CI −3.9% to 3.6%).

In the person time analyses, the incidence of acute lower respiratory tract infections was 0.53 and 0.54 episodes per four month child period of actual follow up in zinc and placebo groups respectively (absolute risk reduction 1%, −2.9% to 5%). As multiple episodes of acute lower respiratory tract infections in a child may not be independent we performed a generalised estimating equations analysis to correct for this correlation. The results of this analysis were similar to those of the uncorrected analysis (odds ratio 0.98, 0.86 to 1.13, table 2).

Pneumonia

Eighty one children in the zinc group and 112 in the placebo group had at least one episode of pneumonia (absolute risk reduction 2.5%, 0.4% to 4.6%). The number needed to treat was therefore 40—that is, supplementation of 40 children would be expected to prevent one child from having from pneumonia.

In the person time analyses, the incidence of pneumonia for the four month child period was similarly lower in the zinc group (absolute risk reduction 2.4%, 0.2% to 4.6%). The findings were similar in the generalised estimating equations analysis (odds ratio 0.74, 0.56 to 0.99, table 2).

The number of children admitted to hospital for any cause was lower in the zinc group (absolute risk reduction 0.6%, −0.5% to 1.8%). Three children, all in the placebo group, died.

Possible limitations of study

As the children in our trial were a representative sample of a well defined low income community, our findings are generalisable to populations with similar dietary and morbidity patterns. We did not include young infants, but recent reports of a decline in mortality in infants aged 1-9 months who were small for gestational age and received zinc supplements suggests benefits at this age, particularly in areas where low birth weight is common.2 As all children in our study received a large dose of vitamin A, the effects reported can only be generalised to such children. Most developing countries supplement children aged 6 months to 5 years with large doses of vitamin A every four to six months.

Radiology, the ideal method for diagnosis of pneumonia, was impractical to use under field conditions. Nevertheless, rigorous training was provided to the study physicians to achieve acceptable levels of variability within and between observers in arriving at the diagnosis. Furthermore, sufficient supplies of syrup were produced at the outset, and all the bottles for a particular child were labelled by a unique child identification number to ensure complete masking of the observers.

Conclusions

The findings of current and previous studies show that improving zinc status in deficient populations should substantially reduce serious morbidity. Prompt measures to improve zinc status are therefore warranted, given the substantial and consistent reduction in severe diarrhoea and pneumonia in supplementation trials. The possible approaches include food fortification, dietary diversification, cultivation of plants that are zinc-dense or have a decreased concentration of zinc absorption inhibitors or supplementation of selected subgroups.