Source and symptoms of COVID-19 among hospital workers in Milan

Background

Healthcare workers (HCWs) are commonly infected by SARS-CoV-2 and represent one of the most vulnerable groups. Adequate prevention strategies are necessary to guarantee HCWs’ safety, as well as to prevent dissemination of the infection among patients.

Aims

To describe a case series of SARS-CoV-2-positive HCWs in a large public healthcare organization in Milan (Italy) during the most devastating weeks of the epidemic and analyse the sources, symptoms and duration of SARS-CoV-2 infection.

Methods

This study included 172 SARS-CoV-2-positive HCWs who were infected between the 25th of February and the 7th of April 2020. A nasopharyngeal swab (NPS) and RT-PCR were used to indicate.

Results

Initially, the most common sources of infection were other positive HCWs (49%). Medical doctors and nursing assistants were most frequently infected, with infection rates of 53/1000 and 50/1000, respectively. COVID-19 departments were less affected than internal medicine, surgery, intensive care, or emergency room. The most commonly reported symptom was mild cough, while loss of smell (anosmia) and loss of taste (ageusia) were reported as moderate and severe by 30–40% of HCWs. The time necessary for 50% of workers to recover from the infection was 23 days, while it took 41 days for 95% of HCWs to become virus-free.

Conclusions

HCWs are commonly infected due to close contacts with other positive HCWs, and non-COVID departments were most affected. Most HCWs were asymptomatic or subclinical but contact tracing and testing of asymptomatic HCWs help identify and isolate infected workers.

Molecular typing of Mycobacterium tuberculosis based on variable number of tandem DNA repeats used alone and in association with spoligotyping

Fingerprinting based on variable numbers of tandem DNA repeats (VNTR), a recently described methodology, was evaluated for molecular typing of Mycobacterium tuberculosis in an insular setting. In this study, VNTR fingerprinting was used alone or as a second-line test in association with spoligotyping, double-repetitive-element PCR (DRE-PCR), and IS6110 restriction fragment length polymorphism (RFLP) analysis, and the discriminatory power for each method or the combination of methods was compared by calculating the Hunter-Gaston discriminative index (HGI). The results obtained showed that in 6 out of 12 (50%) cases, VNTR-defined clusters were further subdivided by spoligotyping, compared to 7 out of 18 (39%) cases where spoligotyping-defined clusters were further subdivided by VNTR. When used alone, VNTR was the least discriminatory method (HGI = 0.863). Although VNTR was significantly more discriminatory when used in association with spoligotyping (HGI = 0.982), the combination of spoligotyping and DRE-PCR (HGI = 0.992) was still the most efficient among rapid, PCR-based methodologies, giving results comparable to IS6110 RFLP analysis. Nonetheless, VNTR typing may provide additional phylogenetical information that may be helpful to trace the molecular evolution of tubercle bacilli.

Molecular basis of IgE cross-reactivity between human beta-casein and bovine beta-casein, a major allergen of milk

Twenty patients allergic to cow's milk proteins and with high levels of specific IgE directed against bovine whole casein were selected to evaluate reactivity of their IgE antibodies with human beta-casein. Highly purified human and bovine beta-caseins were prepared by selective precipitations and FPLC separation. Their identity and purity were assessed by HPLC, analysis of amino acid composition, sequencing of the five N-terminal amino acid residues and immunochemical tests. Direct and indirect ELISAs were performed using human and bovine beta-casein coated into microtiter plates and monoclonal anti-human IgE antibody AChE labelled for revelation. Seven sera contained specific IgE directed against human beta-casein. Inhibition studies using native human and bovine beta-caseins as well as bovine beta-casein-derived peptides demonstrated that, depending on the sera, one or several common epitopes located in different parts of the molecule were shared by the two homologous proteins.

Two-site enzyme immunometric assays for determination of native and denatured beta-lactoglobulin

Two enzyme immunometric assays suitable for measuring native and denatured beta-lactoglobulin (BLg) have been developed. The assays were performed in 96-well microtitre plates and were based on the use of pairs of monoclonal antibodies specific to either the native form or the reduced and carboxymethylated form of BLg (RCM-BLg). Detection limits of 30 and 200 pg/ml were obtained for the native BLg and the RCM-BLg assay, respectively, with very low or negligible cross-reactivity of the other milk proteins and tryptic fragments of BLg. The validity of the assays in different media such as cow's milk and cow's milk products, saline buffer or serum was supported by recovery experiments. The assays were first applied to the determination of BLg and RCM-BLg in PBS and in raw skimmed milk. The ability of the RCM-BLg assay to detect heat-denatured BLg was confirmed by a kinetic study of BLg heat-denaturation in the two media. During heat treatment, the decrease in the concentration of native BLg was associated with an increase in denatured BLg specifically detected by the RCM-BLg assay. By selecting an appropriate monoclonal antibody which failed to recognize caprine BLg, we were able to establish a modified sandwich immunoassay permitting very sensitive detection of cow's milk in goat's milk.