4. Comparison 5. Combination system compared to HVE for reduction in the level of contamination in aerosols.

Combination system compared to HVE for reduction in the level of contamination in aerosols
Population: people undergoing aerosol generating procedures Setting: dental clinic Intervention: combination system Comparison: HVE
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of sites (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with HVE	Risk with combination system
Rate of infection of dental staff or patients	Not reported
Reduction in volume of contaminated aerosols in the operative environment	Not reported
Reduction in level of contamination in aerosols during water spray using high speed handpiece	The mean CFU level was 117.80	MD 109.30 CFU lower (153.01 lower to 65.59 lower)	‐	24 ('n of 1' design) (1 RCT)a	⊕⊝⊝⊝ VERY LOW 1
*The risk in the intervention group (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CFU: colony forming units; CI: confidence interval; MD: mean difference; RCT: randomized controlled trial
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect Moderate certainty: we are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different Low certainty: our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect Very low certainty: we have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect

^aFrere 2016

^1. Downgraded 2 levels for unclear risk of selection bias and high risk of other bias, and 2 levels for imprecision due to small sample size reported in a single study