# Exposure and Health Effects of Bacteria in Healthcare Units: An Overview  
[PERSON]  
1H&TRC--Health & Technology Research Center, ESTeSL--Escola Superior de Tecnologia da Saude, Instituto Politecnico de Lisboa, 1600-560 Lisboa, Portugal; [EMAIL_ADDRESS] (E.R. ); [EMAIL_ADDRESS] (C.V.)  
2 Escola Nacional de Saude Publica, Universidade NOVA de Lisboa, 1600-560 Lisboa, Portugal; [EMAIL_ADDRESS]  
3 Centro de Ciencias e Tecnologias Nucleares (C2 TN), Instituto Superior Tecnico, Universidade de Lisboa, 1600-560 Lisboa, Portugal; [EMAIL_ADDRESS]  
4 Escola Superior de Tecnologia da Saude de Lisboa, Instituto Politecnico de Lisboa, 1600-560 Lisboa, Portugal; [EMAIL_ADDRESS] (J.C.); [EMAIL_ADDRESS] (N.G.) Healthcare units such as hospitals, maternity centers, blood banks, clinics, medical offices, urgent care centers, or healthcare centers consist of countless people circulating daily, such as workers, patients and their companions, the healthy and the sick. These people are vehicles for transmitting microorganisms, such as bacteria, that can cause infections that are transmitted very easily in this setting due to its population of sick or immunocompromised people [6]. Additionally, bacterial contamination in hospitals is heavily affected by the following important factors: construction characteristics, levels of water and nutrients in the interior environment necessary for the growth and survival of bacteria, people that occupy the space, and the outdoor environment [7]. Medical activities, cleaning procedures and their frequency are crucial factors for the increase in bacterial load [8; 9]. Bacterial species have different allergenic, pathogenic, infectious, or toxic properties that can affect humans [10]. Allergenic bacteria, mainly thermophilic bacteria, may generate a hypersensitivity response (hypersensitivity pneumonitis) in the host [10]. A pathogenic bacterium causes disease in a host and is determined by virulence factors, enabling the replication and dissemination of bacteria in the host organism [11; 12]. Bacteria infect a host, usually from another host/reservoir, through direct contact, airborne transmission, a vector, or a common vehicle [10]. In addition, bacteria can produce toxins, which trigger a harmful process in the host organism, inhibiting protein synthesis, activating immune responses, and damaging cell membranes [13]. Bacterial cell wall constituents, such as endotoxins and peptidoglycan, are referred to as agents with pro-inflammatory properties causative of respiratory symptoms (asthma, bronchitis and byssinosis) [10]. The transmission of bacteria can be promoted because healthcare workers interact physically with different patients, unaware that they are transmitting potentially pathogenic agents. Additionally, the handling/contact with contaminated instruments or surfaces [14; 15] can cause a risk of infection in both workers [16] and patients. In fact, the isolation of microorganisms from the surfaces suggests that some patients acquire bacterial infections in the hospital [17; 18; 19; 20]. Hospital-acquired (nosocomial) infections are a concern in terms of patient safety, as they may have a high impact on patient morbidity and mortality [21; 22]. Commonly, most bacteria do not cause adverse health effects and can even benefit us and the environment. The problem arises when the concentration of certain potentially pathogenic bacteria is higher than the infective dose, which varies dramatically across pathogen species [23]. The scale of the severity of the effects on human health depends on many factors such as toxicity, exposure time and microbial load, and even one's age and nutritional status [24]. For example, bacteria such as _Acinetobacter baumannii, Pseudomonas aeruginosa_ and _Stentrorophomonas maltophilian_, which are non-fermenting Gram-negative bacilli, can cause infections and severe health problems.