ObjectiveTo examine a commercially available zinc acetate lozenge for treating the common cold.DesignRandomised, double-blinded, placebo-controlled trial.SettingWorking population in Finland.ParticipantsWe included men and women aged ≥18 years who usually had ≥1 cold per winter. Exclusions were pregnancy, lactation, chronic runny nose or chronic cough.InterventionWe randomised 253 participants to receive a package of lozenges to be taken if they caught the common cold. Of the 253 participants, 88 contracted the common cold and 87 were included in our primary analysis. Zinc acetate lozenges contained 13 mg elemental zinc and placebo lozenges contained sucrose octa-acetate to camouflage the taste of zinc. Instruction to use was six times per day for the maximum of 5 days.Primary outcomeRate of recovery from the common cold analysed by Cox regression.ResultsThere was no difference in the recovery rate between zinc and placebo participants during the 10-day follow-up (rate ratio for zinc vs placebo=0.68, 95% CI 0.42 to 1.08; p=0.10). The recovery rate for the two groups was similar during the 5-day intervention, but for 2 days after the end of zinc/placebo use, the zinc participants recovered significantly slower compared with the placebo participants (p=0.003). In the zinc group, 37% did not report adverse effects, the corresponding proportion being 69% in the placebo group.ConclusionsA commercially available zinc acetate lozenge was not effective in treating the common cold when instructed to be used for 5 days after the first symptoms. Taste has been a common problem in previous zinc lozenge trials, but a third of zinc participants did not complain of any adverse effects. More research is needed to evaluate the characteristics of zinc lozenges that may be clinically efficacious before zinc lozenges can be widely promoted for common cold treatment.Trial registration numberNCT03309995.

The rates of Chlamydia pneumoniae seroconversions suggesting acute primary infections or reinfections and the prevalences of antibodies were followed up among healthy laboratory workers. Annual serum samples were collected from 47 persons in Helsinki from 1958 to 1990 and from 40 persons in Oulu from 1994 to 1999. C. pneumoniae species-specific immunoglobulin G (IgG), IgA, and IgM antibodies were measured by microimmunofluorescence (MIF) in 407 sera from Helsinki. The 185 sera collected in Oulu were tested both by MIF and by commercial enzyme immunoassay (EIA). During the follow-up periods of 31 years in Helsinki and 6 years in Oulu, seroconversions were demonstrated by MIF in 45% and 15% of the study groups, respectively. In Helsinki 9% of the persons seroconverted twice during the follow-up period. By MIF, the total incidence rate per 100 person-years at risk was 6.9 in Helsinki and 4.9 in Oulu, and annual incidence rates varied from 0 to 15.4. By EIA, annual incidence rates in Oulu varied from 0 to 10.8. The seroconversions by MIF were usually not confirmed by EIA and vice versa. Prevalence and persistence rates, respectively, of IgA antibodies were higher in EIA (62% and 26%) than in MIF (26% and 17%), whereas the figures for IgG were quite similar. The prevalence of IgG and IgA antibodies was higher in older persons than in younger ones. The presence of antibodies did not offer protection from reinfection.Chlamydia pneumoniae is a common respiratory pathogen, and almost all people are infected by the age of 20. Seroepidemiological studies have shown that the antibody prevalence rises with age in adult populations (39). Frequent reinfections or persistent infections might explain the higher antibody prevalence in older age groups (13,28,50). C. pneumoniae causes upper and lower respiratory tract infections in humans and causes about 10% of the pneumonia cases in adults worldwide (14, 38). Persistent C. pneumoniae infections have been associated with several chronic diseases, such as asthma (16, 17), chronic obstructive pulmonary disease (47), and coronary heart disease (34,40,41).The epidemiological situation affects the prevalence of C. pneumoniae immunoglobulin G (IgG) and IgA antibodies (25,38). Seroepidemiological surveys have shown that both epidemic and endemic C. pneumoniae respiratory tract infections occur in different parts of the world, and epidemics are more common in sparsely populated areas (38). It has also been suggested that asymptomatic infections or infections with mild respiratory symptoms are common (14). Most transmissions seem to take place at schools, military bases, and workplaces, although the spread of infections at home has also been reported (13,26,39). After an acute infection, IgM titers usually fall within 2 months and normalize within 4 to 6 months. Elevated IgG levels may persist for several years and occasionally be detectable over 3 years after the acute infection (29).At the Department of Virology, University of Helsinki, and at the National Public Health Institute in Oul...