Invasive pulmonary aspergillosis is acquired through inhalation of conidia. Little is known about early interactions between Aspergillus fumigatus conidia and alveolar epithelial cells, so an in vitro model was developed to study binding between conidia and A549 cells, a line of type II pneumocytes. Conidia rapidly became attached to confluent monolayers of A549 cells in serum-free medium, reaching a plateau within 40 min. Scanning electron microscopy (EM) showed a random pattern of early adherence; viable conidia subsequently became clustered on pneumocyte surfaces. Following germination of pneumocyte-adherent conidia for 12 h, direct penetration of epithelial cells by hyphae could be demonstrated by scanning and transmission EM. These data suggest that an early event following inhalation of A. fumigatus conidia may be binding of conidia to pneumocytes, followed by hyphal penetration of the epithelial cell layer.

Aspergillus fumigatus has previously been shown to produce a soluble extracellular inhibitor of the alternative complement pathway, called Aspergillus complement inhibitor, or CI. We now report an efficient method for production of CI which relies on the fact that poorly conidiating cultures yielded CI activity with approximately sevenfold-higher potency than CI produced by conidiating cultures. CI from poorly conidiating cultures provided 50% inhibition of alternative pathway-mediated binding of '25I-labeled complement component C3 to cryptococcal blastoconidia at a mean concentration of 60 ,ug/ml. The ability of crude CI to 3508

Objective: We hypothesized healthcare workers (HCW) with high-risk exposures outside the healthcare system would have less asymptomatic coronavirus 2019 (COVID-19) disease and more symptoms than those without such exposures. Design: A longitudinal point prevalence study during August 17- September 4 2020 and December 2nd - 23rd. Setting: Community based teaching health system Participants: All HCS were invited to participate. Among HCW who acquired COVID-19, logistic regression models were used to evaluate the adjusted odds of asymptomatic disease using high-risk exposure outside the healthcare system as the explanatory variable. The number of symptoms between exposure groups was evaluated with the Wilcoxon rank-sum test. The risk of seropositivity among all HCS by work exposure was evaluated during both periods. Interventions: Survey and serological testing Result: Seroprevalence increased from 1.9% (95% CI 1.2% - 2.6%) to 13.7% (95% CI 11.9% - 15.5%) during the study. Only during Period 2 did HCW with the highest work exposure (versus low exposure) have an increased risk of seropositivity (RD 7% [95% CI 1% -13%]). Participants who had a high-risk exposure outside of work (compared to those without) had a decreased probability of asymptomatic disease (OR 0.38 [95% CI 0.16 – 0.86]) and demonstrated more symptoms (median of 3 [IQR 5] vs 1 [IQR 2]; P = 0.001). Conclusions Health care acquired COVID-19 increases the probability of asymptomatic or mild COVID-19 disease compared to community acquired disease. This suggests infection prevention strategies (including masks and eye protection) may be mitigating inoculum and supports the variolation theory in COVID-19.