In the early 1980s, the National Research Council (NRC) published two reports on chemical safety in laboratories describing the safe handling and disposal of hazardous chemicals in laboratory settings. In response to these two reports, The NRC concluded that a similar document was needed to provide guidance regarding biological safety in laboratories. The Committee on Hazardous Biological Substances in the Laboratory was formed in the fall of 1985 and in 1989, published Biosafety in the Laboratory: Prudent Practices for Handling and Disposal of Infectious Materials. Some 33 years later, biological safety in laboratories continues to be a prime concern.
Clinical laboratories are unique when compared to traditional research laboratories in the sense that every time lab staff handle human samples, workers may or may not be exposed to infectious agents that can harm them or contaminate surrounding areas of the lab.
The risk of laboratory-acquired infections
All infections acquired through laboratories or laboratory-related activities, whether they are symptomatic or asymptomatic in nature, are defined as laboratory-acquired infections (LAIs). The actual risk of LAIs is difficult to quantify because there is no centralized reporting system. Since the first LAI reported in 1885* to 1978, some 4,000 cases of LAIs were reported. However, since the 1970s, broad statistics on LAIs are difficult to find, with most data focused on specific viruses (HIV, Ebola, SARS-CoV-2, etc.).
Pathogenic Organisms Identified in the Wurtz Survey
Number of LAIs
In 2016, Wurtz et al. conducted an international survey of biosafety level 3 and 4 laboratory staff. This survey aimed to determine the number of LAIs that are found in labs that work with highly infectious agents and the possible underlying causes of these infections. The survey found that two of the top causes of LAI are cited as inadequate compliance with safety rules and not wearing personal protective equipment (PPE), suggesting that 78 percent of the LAIs reported in the survey were due to human error. Laboratory technicians were the most commonly infected (87 percent of cases), and the most common route of infection was airborne transmission (87 percent).
Safety measures are critical in an environment where exposure to infectious agents from patient samples can result in serious illness or even death for clinical laboratory staff. The Wurtz study concluded that LAIs with highly pathogenic microorganisms that can result in serious illness (220 cases during the last 35 years) have been infrequent due to the improvement of working conditions and safety measures. Knowing that most LAIs are caused by human error, and that the number of LAIs can be significantly reduced or even eliminated when lab staff follow appropriate safety measures, highlights the need for a culture of safety in clinical laboratories to prevent LAI.
|Most Frequently Reported LAIs Worldwide from 1976 to 1978||Most Frequently Reported LAIs Worldwide from 2002 to 2004|
Number of cases
Number of deaths
Number of cases
Relative risk of infection
|Q fever||280||1||Brucella species||7||8012.5|
|Typhoid fever||258||20||Staphylococcus aureus|
|Venezuelan equine encephalitis||146||1||Escherichia coli O157:H7||2||8.6|
How do you prevent laboratory-acquired infections for each mode of transmission?
Contact transmission: Preventing exposure via the contact route requires staff to work in a manner that avoids contamination of their skin and work surfaces. This is accomplished using gloves, lab coats, and protective sleeves that cover the area between gloves and lab coats, as well as protecting work surfaces with absorbent coverings, cleaning work surfaces, and providing lab staff with proper training in lab procedures. In particular, lab procedures that can generate droplets can easily cause contact exposure. Examples of these procedures include decanting liquids, pipetting, removing caps, vortexing unsealed containers, and streaking inocula on agar plates.
Oral transmission: The procedure with the greatest risk of exposure by ingestion is mouth pipetting. Thankfully, the days of mouth pipetting are long gone, but risk still exists in the clinical lab for ingestion exposure to infectious agents. Indirect exposure can be avoided by frequent hand washing and by not placing anything in the mouth (including fingers) when in the laboratory. In addition, wearing a surgical face mask or a face shield protects staff from accidentally splashing infectious material into their mouths and also prevents them from touching their face or sticking fingers in their mouths.
Ocular transmission: Wearing face shields, safety glasses, or goggles protects lab workers against splashing infectious material into their eyes.
Inoculation transmission: The greatest risk of exposure through inoculation is through the use of needles and syringes in the lab, such as those used to transfer materials from diaphragm-stoppered vials and tubes. Because of the high inoculation risk involved with using these items, the use of needles and syringes should be limited to procedures where there is no alternative. Take great care when using needles and syringes, avoid distractions as much as possible, and always wear a lab coat and gloves.
Respiratory transmission: Several clinical laboratory procedures have the potential to generate aerosols that can be inhaled by lab staff. Some examples include sonication, homogenization, centrifugation, and fluid discharge from pipettes.
Any procedure that has the potential to create hazardous aerosols should be performed inside of a biosafety cabinet while wearing gloves and a lab coat. Class II biosafety cabinets protect workers, the environment, and samples from contamination via HEPA filtration of both the supply and the exhaust air.
Following proper safety precautions is the best defense
LAIs have a been a reality since people first started working in a laboratory setting in the late 1800s. These infections can be very dangerous and even deadly. Clinical lab workers are especially at risk because they often handle large numbers of human samples, and the infectious nature of the samples is often unknown. Taking proper safety precautions when handling potentially infectious material is the only line of defense that clinical lab workers have to protect themselves from these infections.
*Kisskalt, K. Laboratory infections with typhoid bacilli. Z Hyg Und Infectionskrahkh. 1915;80:145–62.