Livestock-associated Staphylococcus aureus in Childcare Worker

To the Editor: Carriage of Staphylococcus aureus sequence type (ST) 398 has primarily been reported as occurring among persons in contact with livestock, including swine and cattle (1,2). This association has given rise to the characterization of this strain as livestock associated (3). However, ST398 colonization or infection in persons lacking identified livestock-associated risk factors have been reported (4,5). We report ST398 colonization in a childcare worker in Iowa, USA. 
 
As part of a surveillance study of S. aureus carriage in child daycare facilities, samples were collected from employees, children, and environmental surfaces. Nasal samples were taken from participating children, and nasal and pharyngeal samples were taken from participating employees. All samples were cultured, and S. aureus isolates were examined by pulsed-field gel electrophoresis, spa typing, and antimicrobial drug susceptibility testing and tested for the Panton-Valentine leukocidin gene. One participant was colonized in the nose and throat with t571, a spa type previously reported to correspond to ST398 (1). The isolates were nontypeable when SmaI was used, also a characteristic of ST398 (6). They were digested with Cfr9I and found to be closely related to an ST398 isolate of spa type t034 of swine origin but distinct from S. aureus isolated from 2 other employees at the facility (Figure). Both ST398 isolates were susceptible to methicillin. 
 
 
 
Figure 
 
Pulsed-field gel electrophoresis of Staphylococcus aureus. Isolates were digested with Cfr9I. Lanes 1 and 7, molecular mass ladder; lane 2, t034 sequence type (ST) 398 isolate from pig; lane 3, t571 ST398 nasal isolate from colonized childcare employee; ... 
 
 
 
The colonized employee was a 24-year-old woman who had worked at the facility for ≈5 years. She reported a history of melanoma but was not currently taking any chemotherapy drugs and had not been hospitalized in the previous 12 months. She reported having a family member who worked in a hospital and had direct contact with patients, but the employee lived alone and responded negatively to questions about whether she or immediate family members had had contact with animals or worked in a processing plant. 
 
ST398 may be transmitted from livestock to community members and then from person to person. It can potentially be transmitted in food; several studies have documented ST398 in raw meats (7,8), and we identified this strain in retail meat products in Iowa (T.C. Smith et al., unpub. data). Secondary transmission of ST398 from colonized persons to contacts has also been suggested, but the few publications reporting this suggest that ST398 seems to be less transmissible by this route than are common human strains (9). 
 
We cannot be sure whether either of these routes played a role in acquisition of ST398 by this employee. Although no other tested persons in this childcare facility were found to carry ST398, only 24 (40%) of the 60 employees and 8 (4.8%) of the 168 children participated, suggesting the possibility of a reservoir in the facility among those who were not tested. Of the 24 employees who participated, 2 reported occupational contact with any animals, 2 reported contact with swine, and 3 reported contact with cattle. However, no participant reported having animals other than cats or dogs on their property. It is possible that >1 sampled employee may have been a transient ST398 carrier but negative at the time of our sampling. 
 
Reports of ST398 in persons who had no direct contact with livestock in the United States are rare (10). To provide a better understanding of the epidemiology of this novel strain, further examination of the emergence of this isolate in community settings and on farms is needed.

rituximab or other immunosuppressive treatments should be prescribed cautiously; the possibility for rare complications should be recognized.
Because of massive ablation of humoral immunity, the relationship between rituximab and virus infection has been addressed, including varicella-zoster infection, parvovirus B19 infection, and CMV reactivation (7). In immunocompromised patients, rituximab might lead to higher risk for virus infection. This issue has been addressed with HIV/AIDS patients with high-grade B-cell lymphoma for whom rituximab is not generally recommended because B-cell ablation could result in more opportunistic infections. For LYG, increased frequency is associated with both congenital and acquired immunodefi ciency, such as X-linked lymphoproliferative syndrome, Wiskott-Aldrich syndrome, and HIV/ AIDS in which T-cell surveillance is defi cient (8). Thus, for a patient with LYG whose immune system might be abnormal (9), the risks associated with rituximab therapy should be considered the same as the risks for HIV/AIDS patients, and the risk for viral infection or reaction to rituximab should be recognized, particularly in areas where CMV seropositivity in the population is high (10). In addition, especially for adult and elderly patients, the gradual increase of CMV seroprevalence with age should be recognized (10). Moreover, the patient reported here had previously received cytotoxic drugs as well as maintenance steroid therapy, both of which contributed to a severely compromised immune system. These factors may have led to her acute CMV pneumonitis after receipt of rituximab.
In conclusion, the potential for acute CMV reactivation should recognized during use of rituximab to treat patients with LYG. During rituximab treatment of LYG, routine monitoring for CMV reactivation and other viral infections is warranted.  (1,2). This association has given rise to the characterization of this strain as livestock associated (3). However, ST398 colonization or infection in persons lacking identifi ed livestock-associated risk factors have been reported (4,5). We report ST398 colonization in a childcare worker in Iowa, USA.

Shang-Gin Wu, Tzu-Hsiu Tsai, and Shang-Ju Wu
As part of a surveillance study of S. aureus carriage in child daycare facilities, samples were collected from employees, children, and environmental surfaces. Nasal samples were taken from participating children, and nasal and pharyngeal samples were taken from participating employees. All samples were cultured, and S. aureus isolates were examined by pulsed-fi eld gel electrophoresis, spa typing, and antimicrobial drug susceptibility testing and tested for the Panton-Valentine leukocidin gene. One participant was colonized in the nose and throat with t571, a spa type previously reported to correspond to ST398 (1). The isolates were nontypeable when SmaI was used, also a characteristic of ST398 (6). They were digested with Cfr9I and found to be closely related to an ST398 isolate of spa type t034 of swine origin but distinct from S. aureus isolated from 2 other employees at the facility (Figure). Both ST398 isolates were susceptible to methicillin.
The colonized employee was a 24-year-old woman who had worked at the facility for ≈5 years. She reported a history of melanoma but was not currently taking any chemotherapy drugs and had not been hospitalized in the previous 12 months. She reported having a family member who worked in a hospital and had direct contact with patients, but the employee lived alone and responded negatively to questions about whether she or immediate family members had had contact with animals or worked in a processing plant.
ST398 may be transmitted from livestock to community members and then from person to person. It can potentially be transmitted in food; several studies have documented ST398 in raw meats (7,8), and we identifi ed this strain in retail meat products in Iowa (T.C. Smith et al., unpub. data). Secondary transmission of ST398 from colonized persons to contacts has also been suggested, but the few publications reporting this suggest that ST398 seems to be less transmissible by this route than are common human strains (9).
We cannot be sure whether either of these routes played a role in acquisition of ST398 by this employee. Although no other tested persons in this childcare facility were found to carry ST398, only 24 (40%) of the 60 employees and 8 (4.8%) of the 168 children participated, suggesting the possibility of a reservoir in the facility among those who were not tested. Of the 24 employees who participated, 2 reported occupational contact with any animals, 2 reported contact with swine, and 3 reported contact with cattle. However, no participant reported having animals other than cats or dogs on their property. It is possible that >1 sampled employee may have been a transient ST398 carrier but negative at the time of our sampling.
Reports of ST398 in persons who had no direct contact with livestock in the United States are rare (10). To provide a better understanding of the epidemiology of this novel strain, further examination of the emergence of this isolate in community settings and on farms is needed. Figure. Pulsed-fi eld gel electrophoresis of Staphylococcus aureus. Isolates were digested with Cfr9I. Lanes 1 and 7, molecular mass ladder; lane 2, t034 sequence type (ST) 398 isolate from pig; lane 3, t571 ST398 nasal isolate from colonized childcare employee; lane 4, t571 ST398 throat isolate from colonized childcare employee; lanes 5 and 6, non-ST398 isolates (t2228 and t084, respectively) from 2 other childcare employees.