HISTORICAL PERSPECTIVE

Review of Laboratory-Acquired Illness

Considerable information has been compiled in recent years from a variety of sources concerning the accidental infection of laboratory workers with pathogenic microorganisms. 

An analysis of available information indicates that about 20% of these infections are due to recognized accidents and that 80% can be attributed to unknown or unrecognized causes.

Over the past 30 years a concerted effort has been made to determine the extent of laboratory-acquired infections.  Studies by many investigators clearly demonstrate that bacterial, fungal, and rickettsial agents are potentially hazardous to individuals within the laboratory, as well as to those in surrounding areas.

The potential for laboratory-acquired viral infections was first addressed in a systematic fashion by in 1951. Investigators, in collaboration with the laboratory branch of the American Public Health Association, initiated a surveillance program to obtain information on laboratory-acquired infections.  This program included the development, distribution, and analysis of a questionnaire that was submitted to over 5,000 laboratories, a search of the published literature, and personal communication.

As of 1996, this registry included in excess of 4,000 cases of laboratory-acquired infections.  Bacterial agents and viruses each accounted for about one third of these illnesses. Rickettsia, fungi, chlamydia and parasites account for the remainder.

It was clear from the cases in this registry ( from and subsequent publications) that the laboratory manipulation of infectious disease agents represents an occupational risk requiring rigorous control to prevent illness and save lives.

It is important to keep in mind that there is no way to determine precisely how many laboratory-acquired infections have occurred or whether all such reported infections were, indeed, laboratory-acquired. 

WHY IS THIS? You might ask.  The answer is quite simple. There are no regulations that require the reporting of laboratory-acquired infections.

The available information has come from cases reported in the scientific literature (approximately two thirds of the cases) and the remainder has come from personal communications and questionnaire responses. 

With these limitations in mind, the analysis of illness due to laboratory exposure has provided information to determine the probable sources of infection, the type of accidents or procedures involved, the work activity that resulted in or was associated with the laboratory illness, and finally, the personnel at risk.

Population at Risk

When the reported episodes were classified according to the primary purpose of the work, it was found that research activity accounted for almost 60% of the infectious episodes; diagnostic work, 17%, biological production, 3.4%; teaching, 2.7%; and the rest could not be classified. 

Comparisons of this kind may be misleading because they do not take into consideration the attack rate (i.e., number stricken divided by the number exposed) of the infections in the various groups, therefore, some caution is warranted.  A reliable calculation of the attack rate would require accurate information on the number of technical people in each activity classification during the period under study, as well as more precise information on the number of laboratory-associated illnesses. 

Approximations have been made, and the estimated attack rates suggest that the risk for researchers is seven to eight times greater than for public health and hospital laboratory workers. 

Estimates, using available United States and European data, indicate that the frequency rate of laboratory-acquired infection is on the order of one to five infections per million working hours.  If we assume that the average laboratory person works 8 hours per day for approximately 225 days (allowing for vacations, holidays, and weekends), then the probability of a laboratory worker acquiring a work-related infection is on the order of 10 ^-2 to 10^-3 . 

It is important to keep in mind that research personnel are more likely to handle more hazardous agents, as well as new or rare agents, and thereby increase the risk for this group of workers.

Data supporting this feature of laboratory-associated illness are presented in the following Table by Percent of Infections

Although trained investigators, technical assistants, animal caretakers, and graduate students experienced over three quarters of the illnesses, the remainder occurred among clerical staff, dishwashers, janitors, and maintenance personnel. 

The first study, reported that of the 368 illnesses evaluated at Fort Detrick, scientific personnel accounted for 82.3%; janitors, dishwashers, and maintenance personnel accounted for 13.7%; and clerical personnel accounted for 3.7% of the illnesses reported. 

These results are consistent with those reported in a second study sponsored by the American Public Health Association.  This latter study, which reviewed 1,286 laboratory infections that occurred in the United States between 1930 and 1950, reported  that 78.1% of the infections occurred in trained personnel, 10.3% in janitors, etc., and 6.6% in clerical personnel.  They also reported that 4.9% of the infections were experienced by students.  Since Fort Detrick was a military facility at the time of the study, few, if any, students were present.

The most significant result which emerges from these studies is that they were performed approximately twenty years apart. During this period all of the concepts for laboratory safety, including safety procedures practices, personnel protection, the use of chemical fume hoods and biosafety cabinets, etc. were introduced into the laboratory work place. This would suggest that laboratory safety with potentially hazardous biological materials is more than having these safety resources available. Most experts agree that it is the proper implementation, use and training of laboratory workers that are the essential elements to prevent laboratory associated illness.