Discussion
Brucellosis is the most common bacterial laboratory-acquired infection
worldwide, owing in part to the low infectious dose and high attack rate
following a laboratory exposure (Blaney, Bosserman, Bui, Guerra, &
Stoddard, 2009). It is also easily aerosolized and has the potential to
cause acute and chronic illness (D L Sewell, 1995). Humans are usually
infected by occupational exposure to infected animals, the consumption
of unpasteurized dairy products from infected animals, or inhalation of
infectious aerosols. Clinical laboratory workers have failed to
recognize suspicious isolates and have manipulated unknown isolates on
open benches, using procedures that could aerosolize brucellae,
increasing their exposure risk to biology hazards (Ackelsberg et al.,
2020). In the present study, eight laboratory-acquired infection events
were found in the southern region, a brucellosis emerging area (Beijing
city). Another event was observed in Ningxia province, which is
historically an area of brucellosis. In the past, more than 90% of
human brucellosis cases in China appeared in the northern animal
husbandry provinces (Shang, Xiao, & Yin, 2002). However, since 2010,
human brucellosis has occurred or reappeared in all provinces in
southern China (Yang et al., 2020). Southern China is an emerging area
of brucellosis with the lowest incidence of brucellosis, but the
incidence is increasing (Yang et al., 2020). In the southern regions,
clinical microbiology laboratories are frequently unfamiliar with the
genus of Brucella, and there is a low index of suspicion by physicians
or failure to notify the laboratory that the handled specimens might
yield a hazardous organism. Typically, clinicians do not consider
brucellosis until notified that bacteremia with Brucella was
suspected. Moreover, the misidentification of the organism by commercial
systems, unsafe laboratory practices, and laboratory accidents have been
responsible for many cases of exposure to the organism and
laboratory-acquired disease in recent years (Yagupsky & Baron, 2005).
In the United States, fewer than 150 cases of brucellosis have been
reported annually since 1986, but brucellosis is among the most commonly
reported laboratory-acquired bacterial infections (Pike, 1976). In
Indiana and Minnesota, two cases of brucellosis in microbiologists at
two clinical laboratories were reported to state health departments in
2006. The results of that investigation showed that Brucella spp.
pose a risk of aerosol-transmitted infection (”Laboratory-acquired
brucellosis–Indiana and Minnesota, 2006,” 2008). Unknown isolates
manipulated and/or tested on open benches was the main risk factor in
the laboratory-acquired infection of brucellosis. In this study, the
problematic current practices when handling blood culture bottles from
patients with fever of unknown origin were the main reason for these
infectious events, and the transmission in our cases was probably due to
aerosol contamination. Similarly, most critical exposures involved
catalase testing or isolate vortexing, both of which may generate
infectious aerosols (Stephanie et al., 2004). In New York City, during
the 2015–2017 period, over 200 occupational exposures occurred when the
unknown isolates were manipulated
and/or tested on open benches, including procedures that could generate
infectious aerosols (Ackelsberg et al., 2020). In Turkey, where
biosafety cabinets do not exist in most hospital laboratories, many
laboratory-acquired Brucella infection events have been reported
(Sayin-Kutlu et al., 2012). In our study, we observed a high risk of
developing laboratory-acquired brucellosis in microbiological laboratory
workers. In Spain, a total of 75 works have suffered from
laboratory-acquired brucellosis, 57% (43/75) of whom were
microbiologists (Bouza, Sánchez-Carrillo, Hernangómez, & González,
2005). Thus, Brucella spp. have persisted as biological hazards
to clinical laboratory workers manipulating unknown clinical isolates.
This suggests that we should improve the ability of clinicians to
diagnose brucellosis, especially in the southern region. Furthermore, it
is essential to promote the use of biosafety level 3 (BSL-3) facilities
when handling specimens from patients suspected of brucellosis
infections and also unidentified isolates. Moreover, the following
practices should be followed: timely exposure risk identification,
information sharing, postexposure prophylaxis (PEP), and appropriate
follow-up of potentially exposed workers, in combination with worker
training to maximize awareness and observance of proper safety
practices. Definitions for the laboratory exposure risk toBrucella spp. and recommendations for PEP have been developed and
applied to the laboratory-acquired brucellosis cases that occurred in
Indiana and Minnesota (Pien, Saah, Miller, & Woods, 2006). Finally, we
consider that the use of gloves, masks, goggles, and a biosafety
cabinet, and also the continuous strengthening of the education on
biosafety of individuals with high infection risk is significant for
preventive laboratory-acquired brucellosis events.
The B. suis strain S2 is a widely used live vaccine in China,
which was isolated from a swine fetus at the Institute of Inspection for
Veterinary Medicine in 1952 (H. Jiang et al., 2018). A study suggested
that the S2 vaccine is of low virulence, stimulates good humoral and
cellular immunity, and protect animals against infection by
heterologous, virulent Brucella species (Zhu et al., 2016). In
the present study, more than 50 individuals infected in the context of
S2 vaccination had clinical manifestations, and 180 persons had no
clinical symptoms. Another study
confirmed that the S2 vaccine had low residual virulence, and the
immunity against the B. melitensis strain induced by S2 had
declined after 150 days more than those of S19 and Rev.1 (Bosseray &
Plommet, 1990). The low residual virulence of S2 may be the main reason
why the patients had no obvious clinical symptoms. Similarly, a B.
abortus S19 vaccine strain was isolated from four persons; all four
infected individuals were employed as milkers and did not have apparent
manifestations of the disease (Osman, Hassan, Ali, Abdoel, & Smits,
2015). Moreover, human illness associated with the vaccine strain RB51
has been documented from inadvertent needle sticks or inoculation of the
conjunctiva or open wounds with RB51 (Ashford et al., 2004; Cossaboom et
al., 2018; Hatcher et al., 2018). The first case of human brucellosis in
Bosnia and Herzegovina was caused by live attenuated Brucella
melitensis Rev.1 strain (Arapovic et al., 2020). Although the vaccine
strain may be transmitted to the human population and may persist in the
blood sometimes without causing overt disease, protective measures
remain important to prevent exposure from vaccine strains. Moreover,
more than 100 grassroots animal epidemic prevention officers from
Ulanqab of Inner Mongolia were diagnosed as having brucellosis from
short-time period, but the conventional serological tests used did not
allow to distinguish between vaccine-associated infection and infections
by contact with infected animals.