Background: Nasal bacterial colonization is often dubbed “asymptomatic.” We hypothesized that rhinitis, common in preschool children, is associated with bacterial colonization and that respiratory viruses, which cause rhinitis, interact with bacteria in ways which promote transmission. Methods: Five hundred eighty-five children (4.2–73.6 months) attending daycare had clinical information, a rhinitis score and nasal swabs collected in February 2009. Swabs in soya tryptone glucose glycerine broth were cultured for Streptococcus pneumoniae (Sp), Haemophilus influenzae (Hi) and Staphylococcus aureus and analyzed by real-time polymerase chain reaction for respiratory viruses, both semiquantitatively. Results: Rhinitis symptoms, carriage of Sp and Hi and viral infection fell, whereas S. aureus carriage rates rose with age. Significant, age-independent associations between rhinitis symptoms and detection of Hi (P < 0.033) and Hi colonization density (P < 0.027) were observed. Of the 42% with detected viruses, most (78%) had picornavirus infection. There was a significant age-independent association between viral infection (and viral load, picornavirus infection and picornaviral load) and detection of Sp (P = 0.020, 0.035, 0.005, 0.014) and between viral infection and viral load and Sp colonization density (P = 0.024, 0.028). Conclusions: Hi may promote its own transmission by inducing or amplifying rhinitis in children. There is a close quantitative relationship between respiratory viral infection, including picornavirus infection and Sp colonization. These findings have implications for understanding disease pathogenesis and formulating prevention strategies using vaccines.

Variation in individual susceptibility or frequency of exposure to infection accelerates the rate at which populations acquire immunity by natural infection. Individuals that are more susceptible or more frequently exposed tend to be infected earlier and hence more quickly selected out of the susceptible pool, decelerating the incidence of new infections as the epidemic progresses. Eventually, susceptible numbers become low enough to prevent epidemic growth or, in other words, the herd immunity threshold (HIT) is reached. We have recently proposed a method whereby mathematical models, with gamma distributions of susceptibility or exposure to SARS-CoV-2, are fitted to epidemic curves to estimate coefficients of individual variation among epidemiological parameters of interest. In the initial study we estimated HIT around 25-29% for the original Wuhan virus in England and Scotland. Here we explore the limits of applicability of the method using Spain and Portugal as case studies. Results are robust and consistent with England and Scotland, in the case of Spain, but fail in Portugal due to particularities of the dataset. We describe failures, identify their causes, and propose methodological extensions.

This study was conducted to evaluate factors affecting the levels of total IgG (tIgG) and measles specific IgG (mIgG) in mother and cord sera, and the efficiency of transplacental transport of tIgG and mIgG. The study was conducted in four hospitals in Oporto, Portugal, where 1539 women and their newborns were enrolled. Measles IgG levels were lower among vaccinated mothers and respective cord sera than among vaccinated counterparts. Cord mIgG was strongly correlated with maternal levels in both vaccinated and unvaccinated groups. Transplacental transport efficiency (TTE) of mIgG decreased with increasing maternal levels, although almost one third of the observed effect was due to measurement error. The TTE was not affected by vaccination status. Monitoring maternal measles antibody levels and maternal vaccination status could be useful to determine when the age for measles vaccination can be reduced.