A throat probiotic that leaves when the lozenges stop

Design

Randomised, non-blinded feasibility trial in primary care

Population

53 adults with two or more sore throats in the preceding three years, south of England

Primary outcome

Prevalence and duration of Streptococcus salivarius K12 colonisation by PCR

Effect

Day 7 colonisation 85.7% daily vs 13.6% weekly; only one participant colonised at day 21 or 35

Fifty-three adults in English primary care, all with at least two sore throats in the past three years, were randomised to Streptococcus salivarius K12 lozenges daily or weekly for 14 days, with whole-mouth swabs by PCR at baseline and on days 2, 7, 14, 21 and 35.

Colonisation was the same in both arms at day 2, around 59 per cent. By day 7 the arms had separated sharply: 85.7 per cent with daily dosing against 13.6 per cent weekly. At day 14 it was 59.1 against 19.1 per cent. After dosing stopped, colonisation vanished — one participant in total was still positive at days 21 and 35.

So if this organism works by occupying the throat, it must be taken continuously, and the effect ends when the lozenges do. Both regimens were easy to follow. This was a feasibility trial designed to choose a dose, and it tells you nothing about whether sore throats are prevented.

• If a patient is already taking this, daily dosing is the regimen with evidence for colonisation.
• Tell them the effect does not persist after stopping; this is not a course of treatment.
• Do not recommend it for preventing sore throat — efficacy has not been tested here.
• Recurrent sore throat still warrants the usual assessment before anything is added.
• Nearly a third of participants failed to return all swabs, which is itself a finding for trial design.

Why it matters

It turns a supplement sold as a course into one that only works while it is being taken.

Don't overread it

A feasibility trial of colonisation and acceptability; no sore throat outcome was measured.

The statistics, in plain English

With around 22 participants per arm, the confidence intervals are very wide — day 7 weekly colonisation of 13.6 per cent carries an interval from 0 to 28 per cent. The day 7 separation between arms is nonetheless large enough that imprecision does not threaten the direction. A feasibility trial has no power calculation for clinical outcomes and reports none.

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