IntroductionSample stability can be influenced by many different factors; evaporation and leakage from residual cells are the most relevant factors for electrolytes. During the analytical phase, samples are usually kept uncapped at room temperature. Once samples are processed, they are usually stored sealed and refrigerated. Long turnaround time and the possibility of “add-on test” need consideration for electrolyte stability. The aim of our study is to examine short-term electrolyte stability in this two-common laboratory working conditions in two different lithium heparin plasma tubes (Barricor and PST II, Becton Dickinson).Materials and methodsIn 39 plasma samples from voluntary subjects we measured sodium (Na+), potassium (K+) and chloride (Cl–) at 6 time points since centrifugation (0h, 3h, 6h, 9h, 12h and 15h). Maximum allowable bias (clinically significant change) was based in SEQC (Sociedad Espańola de Química Clínica) recommendations; 1% for Cl–, 0.6% for Na+ and 4% for K+.ResultsIn open room temperature tubes, clinically significant changes appeared in Na+ and Cl– after 3 hours and in K+ after 9 hours in both types of tubes. In refrigerated sealed tubes, all the analytes were clinically stable up to 12 hours in both kinds of plasma tubes. We observed a statistically significant progressive increase in K+ levels, which was less pronounced in Barricor tubes.ConclusionStability of electrolytes is compromised after 3 hours in open tubes and after 12 hours in sealed tubes.

Background: At the time of our study, occupational health evidence specific for long-term care employees was mostly lacking. The purpose of this study was to determine the proportion of positive cases in employees after the first COVID-19 wave in May 2020. We also determined the prevalence of asymptomatic cases. Method: The study population included all health care workers (HCW) employed at one mid-size long-term hospital in Spain (May 2020). A cross-sectional study design included an interviewer-administered self-reported questionnaire (including sociodemographic questions, risk factors for COVID-19 complications such as hypertension or diabetes, and previous polymerase chain reaction [PCR] results) and antibody determination (Biozek rapid test). Data were analyzed using Student’s t, Fisher, and chi-square tests. Two multivariate logistic models were created to evaluate exposure factors and symptoms separately on the outcome of having had COVID-19. Findings: Of the 97% of workers who participated (580/596), 300 (51.7%) suffered symptoms of COVID-19, 161 (27.8%) of the rapid antibody tests were positive for IgM and/or IgG, 160 (27.6%) workers had at least one risk factor, and 32 (19.0%) of the 168 SARS-CoV-2-positive cases were asymptomatic. The proportion of negative or unavailable PCRs, with positive antibody, was 11.7% (56/477). Casual contact without protection (odds ratio [OR]: 1.9, 95% confidence interval [CI]: 1.1–3.4), doctor occupation (OR 3.3, 95% CI: 1.1–10.2), and nursing assistant occupation (OR 2.5, 95% CI: 1.2–5.8) were independently associated with SARS-CoV-2 infection. Conclusion: Physicians and nursing assistants in a long-term care setting were at a higher risk of SARS-COV-2 infection over other occupations in the first wave of the pandemic, especially when in contact with patients without protection. Almost one-fifth of the workers with a positive PCR test for SARS-COV-2 were asymptomatic and seroprevalence (27.8%) was well below the approximated herd immunity cutoff (60–70%). Essential workers in long-term care must be monitored frequently by Employee Health Service and should be required to wear personal protective equipment including a fit-tested N-95 while in close contact with patients and coworkers.

2AbstractAs COVID-19 vaccine research efforts seem to be yielding the first tangible results, the proportion of individuals needed to reap the benefits of herd immunity is a key element from a Public Health programs perspective.This magnitude, termed the critical immunization threshold (q), can be obtained from the classical SIR model equilibrium equation, equaling (1 − 1/R0)/ ϵ, where R0 is the basic reproduction number and ϵ is the vaccine efficacy. When a significant proportion of the population is already immune, this becomes (n − 1/R0)/ ϵ, where n is the proportion of non-immune individuals. A similar equation can be obtained for short-term immunization thresholds(qt), which are dependent on Rt.qs for most countries are between 60-75% of the population. Current qt for most countries are between 20-40%.Therefore, the combination of gradual vaccination and other non-pharmaceutical interventions will mark the transition to the herd immunity, providing that the later turns out to be a feasible objective. Nevertheless, immunization through vaccination is a complex issue and many challenges might appear.