Background: Knowing the prevalence of true asymptomatic coronavirus disease 2019 (COVID-19) cases is critical for designing mitigation measures against the pandemic. We aimed to synthesize all available research on asymptomatic cases and transmission rates. Methods: We searched PubMed, Embase, Cochrane COVID-19 trials, and Europe PMC for primary studies on asymptomatic prevalence in which (1) the sample frame includes at-risk populations and (2) follow-up was sufficient to identify pre-symptomatic cases. Meta-analysis used fixed-effects and random-effects models. We assessed risk of bias by combination of questions adapted from risk of bias tools for prevalence and diagnostic accuracy studies. Results: We screened 2,454 articles and included 13 low risk-of-bias studies from seven countries that tested 21,708 at-risk people, of which 663 were positive and 111 asymptomatic. Diagnosis in all studies was confirmed using a real-time reverse transcriptase–polymerase chain reaction test. The asymptomatic proportion ranged from 4% to 41%. Meta-analysis (fixed effects) found that the proportion of asymptomatic cases was 17% (95% CI 14% to 20%) overall and higher in aged care (20%; 95% CI 14% to 27%) than in non-aged care (16%; 95% CI 13% to 20%). The relative risk (RR) of asymptomatic transmission was 42% lower than that for symptomatic transmission (combined RR 0.58; 95% CI 0.34 to 0.99, p = 0.047). Conclusions: Our one-in-six estimate of the prevalence of asymptomatic COVID-19 cases and asymptomatic transmission rates is lower than those of many highly publicized studies but still sufficient to warrant policy attention. Further robust epidemiological evidence is urgently needed, including in subpopulations such as children, to better understand how asymptomatic cases contribute to the pandemic.

Background:The prevalence of true asymptomatic COVID-19 cases is critical to policy makers considering the effectiveness of mitigation measures against the SARS-CoV-2 pandemic. We aimed to synthesize all available research on the asymptomatic rates and transmission rates where possible. Methods:We searched PubMed, Embase, Cochrane COVID-19 trials, and European PMC for preprint platforms such as MedRxiv. We included primary studies reporting on asymptomatic prevalence where: (a) the sample frame includes at-risk population, and (b) there was sufficiently long follow up to identify pre-symptomatic cases. Meta-analysis used fixed effect and random effects models.Results: We screened 571 articles and included five low risk-of-bias studies from three countries (China (2), USA (2), Italy (1)) that tested 9,242 at-risk people, of which 413 were positive and 65 were asymptomatic. Diagnosis in all studies was confirmed using a RT-qPCR test. The proportion of asymptomatic cases ranged from 6% to 41%. Meta-analysis (fixed effect) found that the proportion of asymptomatic cases was 16% (95% CI: 12% -20%) overall; higher in non-aged care 19% (15% -24%), and lower in long-term aged care 8% (4% -14%). Two studies provided direct evidence of forward transmission of the infection by asymptomatic cases but suggested lower rates than symptomatic cases. Conclusion:Our estimates of the prevalence of asymptomatic COVID-19 cases are lower than many highly publicized studies, but still substantial. Further robust epidemiological evidence is urgently needed, including in sub-populations such as children, to better understand the importance of asymptomatic cases for driving spread of the pandemic.

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Objective: Design, setting and participants: Cross‐sectional survey of Sydney residents during WHO Phase 5 of pandemic (H1N1) 2009. Members of the public were approached in shopping and pedestrian malls in seven areas of Sydney between 2 May and 29 May 2009 to undertake the survey. The survey was also made available by email. Main outcome measures: Perceived personal risk and seriousness of the disease, opinion on the government and health authorities’ response, feelings about quarantine and infection control methods, and potential compliance with antiviral prophylaxis. Results: Of 620 respondents, 596 (96%) were aware of pandemic (H1N1) 2009, but 44% (273/620) felt they did not have enough information about the situation. More than a third (38%; 235/620) ranked their risk of catching influenza during a pandemic as low. When asked how they felt pandemic influenza would affect their health if they were infected, only a third (33%; 206/620) said “very seriously”. Just over half of the respondents (58%; 360/620) believed the pandemic would be over within a year. Respondents rated quarantine and vaccination with a pandemic vaccine as more effective than hand hygiene for the prevention of pandemic influenza. Conclusions: Emphasising the efficacy of recommended actions (such as hand hygiene), risks from the disease and the possible duration of the outbreak may help to promote compliance with official advice.

Objective: To describe antimicrobial resistance and molecular epidemiology of methicillin‐resistant Staphylococcus aureus (MRSA) isolated in community settings in Australia. Design and setting: Survey of S. aureus isolates collected prospectively Australia‐wide between July 2004 and February 2005; results were compared with those of similar surveys conducted in 2000 and 2002. Main outcome measures: Up to 100 consecutive, unique clinical isolates of S. aureus from outpatient settings were collected at each of 22 teaching hospital and five private laboratories from cities in all Australian states and territories. They were characterised by antimicrobial susceptibilities (by agar dilution methods), coagulase gene typing, pulsed‐field gel electrophoresis, multilocus sequence typing, SCCmec typing and polymerase chain reaction tests for Panton–Valentine leukocidin (PVL) gene. Results: 2652 S. aureus isolates were collected, of which 395 (14.9%) were MRSA. The number of community‐associated MRSA (CA‐MRSA) isolates rose from 4.7% (118/2498) of S. aureus isolates in 2000 to 7.3% (194/2652) in 2004 (P = 0.001). Of the three major CA‐MRSA strains, WA‐1 constituted 45/257 (18%) of MRSA in 2000 and 64/395 (16%) in 2004 (P = 0.89), while the Queensland (QLD) strain increased from 13/257 (5%) to 58/395 (15%) (P = 0.0004), and the south‐west Pacific (SWP) strain decreased from 33/257 (13%) to 26/395 (7%) (P = 0.01). PVL genes were detected in 90/195 (46%) of CA‐MRSA strains, including 5/64 (8%) of WA‐1, 56/58 (97%) of QLD, and 25/26 (96%) of SWP strains. Among health care‐associated MRSA strains, all AUS‐2 and AUS‐3 isolates were multidrug‐resistant, and UK EMRSA‐15 isolates were resistant to ciprofloxacin and erythromycin (50%) or to ciprofloxacin alone (44%). Almost all (98%) of CA‐MRSA strains were non‐multiresistant. Conclusions: Community‐onset MRSA continues to spread throughout Australia. The hypervirulence determinant PVL is often found in two of the most common CA‐MRSA strains. The rapid changes in prevalence emphasise the importance of ongoing surveillance.

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Objective: To describe the frequency, cause and potential cost of prevention of hollow‐bore dirty needlestick injury (NSI) sustained by healthcare workers. Design and participants: Ten‐year prospective surveillance study, 1990–1999, with triennial anonymous questionnaire surveys of nursing staff. Setting: 800‐bed university tertiary referral hospital in Brisbane, Australia. Main outcome measures: Rates and circumstances of NSI in medical, nursing and non‐clinical staff; knowledge of NSI consequences in nurses; and minimum costs of safety devices. Results: Between 1990 and 1999, there was a significant increase (P < 0.001) in the trend of the reported rate of NSI. Of the 1836 “dirty” NSIs reported, most were sustained in nursing (66.2%) and medical (16.8%) staff, with 62.7% sustained before disposal. Hollow‐bore injuries from hypodermic needles (83.3%) and winged butterfly needles (9.8%) were over‐represented. Knowledge among nursing staff of some of the risks and outcomes of NSI improved over the decade. A trend (χ2 = 9.89; df = 9; P = 0.0016) with increasing rate of reported injuries in this group was detected. The estimated cost of consumables only, associated with the introduction of self‐retracting safety syringes with concomitant elimination of butterfly needles, where practicable, would be about $365 000 per year. Conclusion: More than one NSI occurs for every two days of hospital operation. Introduction of self‐retracting safety syringes and elimination of butterfly needles should reduce the current hollow‐bore NSI by more than 70% and almost halve the total incidence of NSI.