Three, if by air

Pulmonary injury after combined exposures to low-dose low-LET radiation and fungal spores

Exposure to infectious microbes is a likely confounder after a nuclear terrorism event. In combination with radiation, morbidity and mortality from an infection may increase significantly. Pulmonary damage after low-dose low-LET irradiation is characterized by an initial diffuse alveolar inflammation. By contrast, inhaled fungal spores produce localized damage around pulmonary bronchioles. In the present study, we assessed lung injury in C57BL/6 mice after combined exposures to whole-body X radiation and inhaled fungal spores. Either animals were exposed to Aspergillus spores and immediately irradiated with 2 Gy, or the inoculation and irradiation were separated by 8 weeks. Pulmonary injury was assessed at 24 and 48 h and 1, 2, 4, 8, and 24 weeks later using standard H&E-stained sections and compared with sham-treated age-matched controls. Immunohistochemistry for invasive inflammatory cells (macrophages, neutrophils and B and T lymphocytes) was performed. A semi-quantitative assessment of pulmonary injury was made using three distinct parameters: local infiltration of inflammatory cells, diffuse inflammation, and thickening and distortion of alveolar architecture. Radiation-induced changes in lung architecture were most evident during the first 2 weeks postexposure. Fungal changes were seen over the first 4 weeks. Simultaneous combined exposures significantly increased the duration of acute pulmonary damage up to 24 weeks (P < 0.01). In contrast, administration of the fungus 8 weeks after irradiation did not produce enhanced levels of acute pulmonary damage. These data imply that the inhalation of fungal spores at the time of a radiation exposure alters the susceptibility of the lungs to radiation-induced injury.

Positive-pressure isolation and the prevention of invasive aspergillosis. What is the evidence?

Positive-pressure ventilation implies a sealed room, usually with an anteroom to facilitate the donning of protective clothing, airflows of at least 12 air changes per hour and high-efficiency particulate air (HEPA) to prevent infection in susceptible patients. Laminar airflow (LAF) involves much greater air changes, expense and inconvenience to the patient due to noise and draughts. There are few, if any, truly controlled trials on the impact of positive-pressure ventilation and the prevention of invasive aspergillosis (IA); most are observational studies conducted during an outbreak or retrospective analyses of the incidence of IA over periods of time when a variety of preventative interventions were introduced. Therefore, it is often difficult to determine the specific impact of positive-pressure ventilation with HEPA in leading to a reduction in IA. During periods of hospital demolition or construction, HEPA significantly reduces the aspergillus spore counts and in many studies, the incidence of IA, but other measures such as enhanced cleaning, the sealing of windows and the use of prophylactic anti-fungal agents are also important. On balance, the additional expense and inconvenience of LAF does not appear to be justified. Where positive-pressure ventilation is installed, it is imperative that the system be monitored to ensure that the pressure differentials and air changes are appropriate. Whilst there is a role for positive-pressure ventilation in reducing the incidence of IA, we need a better definition of the importance of hospital-acquired IA compared with community-acquired infection and of the relationship between strains of Aspergillus species isolated from the environment and those strains causing infection.