**3. Results**

The systematic literature search of the non-Chinese databases uncovered 4038 titles, and 15 were included after subsequent review of abstracts and full manuscripts for inclusion and exclusion criteria (Figure 1) [5–7,12–23]. Of the included studies, 13 were conducted in a hospital setting and two assessed episodes occurring in the community. Included studies were conducted in sites located within 10 countries: India (*n* = 6); Bangladesh (*n* = 5); Nepal (*n* = 1); Turkey (*n* = 1); Brazil (*n* = 1); Pakistan (*n* = 1); Ethiopia (*n* = 1); Yemen (*n* = 1); and Poland (*n* = 1). These studies enrolled a total of 3271 zinc-allocated and 3314 placebo-allocated diarrhea cases. The systematic literature search for Chinese studies resulted in 1520 titles, of which 89 were included (Figure 1) [24–112]. All included studies were conducted in a hospital setting, and 33 studies focused on diarrhea attributable to laboratory confirmed rotavirus. None of the included studies identified through the Chinese database were placebo-controlled; for Chinese studies, zinc and control groups received a range of supportive treatments, including fluid infusion, probiotics and antivirals. The total enrolment of included Chinese studies was 6198 zinc group and 6039 control group diarrhea cases. Table 1 describes the trial setting, sample size, and zinc intervention for all included studies.

**Figure 1.** Results of systematic literature search and review.


**Table 1.** Characteristics of included studies.


**Table 1.***Cont.*


**Table 1.** *Cont.*


**Table 1.** *Cont.*


**Table 1.** *Cont.*


**Table 1.***Cont.*


**12** 

> **Table 1.** *Cont.*


\* Study not included in dose analyses.

**13** 

> **Table 1.** *Cont.*

The results of the studies identified through non-Chinese databases are summarized in Tables 2 and 3. Acute episodes were 4% (95% CI: 1%–8%) shorter in duration among children treated with zinc compared to those receiving placebo (Table 2). Among children hospitalized for diarrhea, the duration of hospitalization was reduced by 37% (95% CI: 21%–53%) comparing the zinc and control groups (Table 2). Stool frequency was decreased by 6% (95% CI: 2%–10%) among zinc-treated children. Zinc-treated children had a reduced relative risk (RR) of acute diarrhea lasting beyond three and seven days and an increased risk of vomiting (RR: 1.83; 95% CI: 1.40–2.39) (Table 3).


**Table 2.** Pooled means of select outcomes for non-Chinese studies.

1 Individual studies may contribute more than one study site (*N*) to each estimate; <sup>2</sup> Estimates for study sites generated by Poisson regression model weighted by sample size; <sup>3</sup> Percent difference calculated by: 100 × ((Pooled Zinc Estimate í Pooled Control Estimate)/Pooled Control Estimate); 95% CI calculated by: Percent Difference ± 1.96 × {|(meanzinc/meancontrol)| × sqrt[(std errorzinc) 2 /(meanzinc) 2 + (std errorcontrol) 2 /(meancontrol) 2 ]} × 100.


**Table 3.** Pooled relative risk of select outcomes for non-Chinese studies.

1 Individual studies may contribute more than one study site (*N*) to each estimate; <sup>2</sup> Estimates for study sites generated by logistic regression model weighted by sample size; <sup>3</sup> Estimates for VWXGLHV generated by random effects meta-analysis.

Outcomes pooled across studies conducted in China showed reductions in the duration of diarrhea, hospitalization, fever, vomiting, stool output and stool frequency among zinc-treated children with acute diarrhea attributable to rotavirus and to non-specific causes (Table 4). The reduction in the duration of diarrhea was 37% (95% CI: 35%–39%) among non-specific episodes and 31% (95% CI: 29%–34%) among rotavirus episodes (Table 4). The RR of diarrhea lasting beyond three days was reduced among zinc-treated patients with non-specific (RR: 0.73; 95% CI: 0.66–0.79) and rotavirus (RR: 0.70; 95% CI: 0.63–0.78) diarrhea (Table 5; Figures 2 and 3).


**Table 4.** Pooled means of select outcomes for Chinese studies.

1 Individual studies may contribute more than one study site (*N*) to each estimate; <sup>2</sup> Estimates for VWXG\ VLWHV generated by Poisson regression model weighted by sample size; <sup>3</sup> Percent difference calculated by: 100 × ((Pooled Zinc Estimate í Pooled Control Estimate)/Pooled Control Estimate); 95% CI calculated by: Percent Difference ± 1.96 × {|(meanzinc/meancontrol)| × sqrt[(std errorzinc) 2 /(meanzinc) 2 + (std errorcontrol) 2 /(meancontrol) 2 ]} × 100.


**Table 5.** Pooled relative risk of select outcomes for Chinese studies.

1 Individual studies may contribute more than one study site (*N*) to each estimate; <sup>2</sup> Estimates for study sites generated by Poisson regression model weighted by sample size; <sup>3</sup> Estimates for VWXGLHV generated by random effects meta-analysis.

We did not identify any studies reporting diarrhea-specific or all-cause mortality for inclusion in this review. Nor did we identify non-Chinese studies reporting duration of fever or vomiting, or Chinese studies reporting the proportion of children vomiting.

The mean episode duration and proportion of episodes lasting >3 days were not statistically significantly different comparing zinc-treated children in Chinese and non-Chinese studies. There was no statistically significant difference between the estimated relative risk of an episode lasting >3 days (RRR: 1.07; 95% CI: 0.90–1.27) comparing Chinese and non-Chinese studies; therefore, we pooled this outcome across regions (RR: 0.74; 95% CI: 0.68–0.80) (Figure 3). The percentage difference between the mean episode duration of zinc-treated and control group children was statistically significantly larger for Chinese compared to non-Chinese studies (*p* < 0.05), so this

outcome was not pooled across regions. We did not have sufficient power to compare other commonly reported outcomes by region.

**Figure 2.** Forest plot for the effect of therapeutic zinc supplementation on Rotavirus diarrhea episodes >3 days.

Zinc dose was not associated with the mean percent difference in diarrhea duration comparing zinc and control children for non-Chinese (*p* = 0.50) or Chinese (*p* = 0.12) studies. Comparing Chinese studies that used Licorzinc to those that used other zinc supplements, there were no statistically significant differences in the mean percent difference in the duration of rotavirus episodes (*p* = 0.56), the RR of non-specific episodes lasting >3 days (RRR: 0.99; 95% CI: 0.72– 1.35), or the RR of rotavirus episodes lasting >3 days (RRR: 0.93; 95% CI: 0.68–1.26). The percentage difference in the mean duration of non-specific episodes comparing zinc and control group children was statistically significantly higher for Licorzinc compared to "other zinc" studies (*p* = 0.01).

Our assessment of publication bias yielded largely symmetrical funnel plots for all outcomes.

Under the CHERG grading system, the studies included in this review were of moderate quality (Table 6) [11]. Effect estimates were largely consistent in directionality for all outcomes.

**Figure 3.** Forest plot for the effect of therapeutic zinc supplementation on non-specific diarrhea episodes lasting >3 days.



**Table 6.** *Cont.*

### **4. Discussion**

The findings of our systematic review confirm and highlight the benefits of therapeutic zinc supplementation for diarrhea among children under five years of age in low- and middle-income countries. The effects of zinc treatment, which include reductions in episode duration, stool output, stool frequency and length of hospitalization, were consistent across Chinese and non-Chinese studies and non-specific and rotavirus diarrhea. These results suggest that zinc therapy of diarrhea is largely beneficial and important in both low- and middle-income settings.

The results of the large number of Chinese trials in rotavirus diarrhea are a substantial addition to the global evidence base because there have been no non-Chinese trials. One study in India based on a post-hoc subgroup analysis suggested that zinc treatment was not beneficial for rotavirus diarrhea [113]; however, the evidence from China demonstrates that therapeutic zinc supplementation reduces the duration and severity of rotavirus episodes. As rotavirus is the predominant cause of severe acute diarrhea worldwide and most likely the leading cause of diarrhea mortality [114], zinc treatment of rotavirus diarrhea could potentially yield large reductions in hospitalizations and deaths.

In comparison to non-Chinese studies, the difference between the mean episode duration of zinctreated and control group children was statistically significantly higher for Chinese studies (*p* < 0.05). It is possible that this difference resulted from lack of placebo-controlled groups and blinding among Chinese studies. However, estimates of the effects of therapeutic zinc supplementation on other outcomes were largely consistent across study locations and we were able to generate a pooled global effect size for the proportion of episodes >3 days. The consistency of effect estimates between studies conducted in and outside China suggests that the lack of placebo-controlled groups in Chinese studies did not greatly bias the results.

Zinc dose did not affect the estimate of the effect of zinc supplementation on the duration of diarrhea for non-Chinese or Chinese studies. Although Licorzinc was associated with slightly greater reductions in the mean duration of non-specific diarrhea than other zinc products, zinc effect sizes were generally comparable across Chinese studies regardless of type of zinc preparation.

There is a dearth of literature meeting our inclusion criteria that assessed diarrhea-specific and all-cause mortality. Although a previous review published mortality effect estimates [4], the sole study reporting diarrhea-specific deaths was cluster-randomized and thus violated our inclusion criteria [115]. In addition, three studies of all-cause mortality were also excluded from our review; one was on persistent diarrhea [116], and two others were review papers [3,117].

Using previously published scoring criteria, the studies included in our review yielded pooled estimates of overall moderate quality [11]. The majority of studies contributing to this review were conducted in China and South Asia; however, studies conducted outside Asia were consistent in the directionality of effect estimates. The consistency and quality of all outcomes bolsters the evidence in support of oral zinc supplementation for the treatment of acute diarrhea among children under five in low- and middle-income countries.
