Investigation and control of a Shigella sonnei outbreak in a day care center.

Shigella organisms are invasive, Gram negative, facultative enterobacteria that are harbored in the intestinal tract of humans and transferred by the fecal-oral route. Shigella dysenteriae, Shigella flexneri, Shigella boydii and Shigella sonnei constitute the four species of the genus. Speciation is based upon serological and biochemical reactions. All four species can cause shigellosis, but the severity of the disease, mortality and frequency of isolation differ for each species (1).

Shigellosis or bacillary dysentery is characterized by fever, painful, watery diarrhea, and as the infection proceeds, the feces are tinged with blood, mucus and polymorphonuclear leukocytes (1). Dehydration accompanied by electrolyte imbalance is the primary concern with this illness, especially in children. Asymptomatic cases do occur (2).

Less than 200 ingested Shigella organisms can be sufficient to initiate infection. The organism is quite virulent. Some studies indicate that as few as 10 to 100 colony-forming units can cause infection (2,3). Individuals primarily responsible for transmission are those who fail to clean hands and under fingernails thoroughly after defecation. They may then spread infection to others by direct physical contact or indirectly by contaminating food or utensils (2). Shigella bacteria can survive for an extended period of time on fomites (3). The incubation period is usually 36 to 72 hours (4).

The organism enters the small intestine, multiplies and produces an enterotoxin that is thought to be responsible for the watery diarrhea that occurs at this stage. The bacteria proceed to the terminal ileum and colon where they penetrate the epithelial cells and again multiply, resulting in mucosal ulceration and formation of small abscesses. This is the period of dysentery or passage of blood and mucus. Shigella bacteria seldom completely penetrate the intestinal wall.

During acute infection, as many as |10.sup.6~ to |10.sup.10~ organisms per gram of stool can be detected (4). The patient is infectious until the organisms are no longer present in the feces. Interestingly, in previously healthy adults, spontaneous cure can occur within two to seven days (1). However, studies have shown asymptomatic carriers may transmit infection for as long as 60 days or possibly longer (2).

Diagnosis is made by identification of the bacilli from a stool sample or rectal swab. When stool samples are taken, the time interval between collection and inoculation of media must be limited. The time minimization is needed because of the Shigella organism's sensitivity to the acids present in the feces (1).

Shigella sonnei has persistently accounted for 60 to 80 percent of all shigellosis cases in the United States over the last two decades (1,4). Two-thirds of these cases are in children under 10 years of age (2).

The following history describes a Shigella sonnei outbreak in a licensed day care center and the methods used to determine the source of the pathogen. Techniques used to control the spread of the disease are also discussed.

Methods

On April 2, 1992 a physician in Garland, Texas reported a laboratory-confirmed case of shigellosis to the Garland Health Department (GHD). The causative agent was Shigella sonnei. The patient was a five year old black female. She had experienced severe diarrhea and a low grade fever on March 28. The attending physician began treatment with antibiotics. The child returned to public schools and private day care on March 30, 1992 after symptoms had diminished.

GHD officials visited the day care center on April 7 when it was determined that the child spent approximately three hours at the day care center after attending kindergarten in the public schools. Daily attendance at the day care center was approximately 144 children, ranging in age from infant to pre-teen. The child was grouped with the other "young after schoolers" and provided snacks and refreshments when she arrived. The director of the day care center was given information on shigellosis and was told to increase awareness of personal hygiene with the staff and also with the students. The director was also reminded to exclude all diarrhea cases from the center and to call the GHD if any suspicious cases appeared. No announcement was given to the parents of children in the center. The Garland Independent School District (GISD) received notification at this time. The epidemiological investigation revealed no recollection from the parents of any possible source contacts. The GISD clinical staff and the day care center staff also could not recall any other children exhibiting symptoms similar to the patient's.

On April 21, 1992 the director of the day care center contacted the GHD with another confirmed case of Shigella sonnei. This student, like the first, had severe diarrhea and a mild fever, and was treated successfully with antibiotics. The patient was a 13-year-old black male whose mother was a teacher at the center and who occasionally stayed at the center with the "older after schoolers." These students also received a snack and refreshments.

Fearing the day care center was now possibly the source of the second case of Shigella, on April 21 the GHD issued a Health Bulletin to all parents of children attending the center. The bulletin told parents of the two confirmed cases of shigellosis and explained the disease, its transmission and methods of preventing the spread of the infection. Once again, the director was instructed to exclude all diarrhea cases from the center and to call the GHD if any suspicious cases appeared.

On April 22, 1992 a four-year-old white female was excluded with severe diarrhea and fever. Lab tests confirmed on May 1, 1992 the patient's stool to be positive for shigella sonnei. The mother of this child also became ill on April 24 with diarrhea and a mild fever. Both were treated with antibiotics and recovered quickly.

On April 24, a 27-year-old white female, who was employed as a substitute

teacher at the day care center, became ill with bloody diarrhea and fever. On May 1, the illness was confirmed to be Shigella sonnei. A six-year-old black female was excluded with diarrhea and fever on April 27. The parents refused to get a physician's clearance and thus she was not allowed to re-enter the day care center.

On May 1, the director, a 26-year-old white female, reported bloody diarrhea, severe cramps and fever. Her physician treated her clinically with antibiotics and she returned to work three days later.

The GHD issued a Health Order on May 5, 1992 in an attempt to minimize the spread of shigellosis in the day care center. The Health Order consisted of seven requirements:

* Immediately cease all new enrollment.

* By May 8, 1992 provide to the GHD stool samples for all staff members.

* Immediately exclude any child or staff member who develops diarrhea.

* Excluded staff members or children may be readmitted only when they present evidence of a negative stool culture.

* Any person exhibiting a positive culture for Shigella may only be readmitted with approval of GHD.

* Notify the GHD of all suspected Shigella cases.

* Observe strict hand washing techniques. All staff members must use either an iodine surgical soap or an alcohol foam soap disinfectant after hand washing.

On May 7, an eight-year-old white female was excluded with severe pus-laden diarrhea, cramps and high fever (104 |degrees~ F). She was stool-positive for Shigella sonnei. Over the next 10 days, seven other children were excluded from the day care center because they exhibited diarrhea.

From May 6 to May 8, the GHD collected stool samples from 19 of the 20 staff members. One male staff member refused to submit a sample and was not allowed to return to the day care center. The stool samples were tested at a local hospital laboratory for the presence of Shigella.

Results

On May 11, 1992 the laboratory informed the GHD that a stool culture of one staff member had tested positive for Shigella sonnei. All other staff stool samples submitted were negative for pathogens. The patient was a 30-year-old white female whose primary duty at the day care center was food preparation. The patient reported that she had never experienced any symptoms associated with shigellosis.

Immediately after notification from the laboratory, GHD excluded the food handler from the day care center. She began antibiotic treatment on May 11. Before the patient could return to work, successive fecal samples taken 24 hours apart and begun 48 hours after discontinuance of antibiotics were required to be free of Shigella sonnei.

On May 26, after two negative stool cultures, the food handler was allowed to resume her duties at the day care center. On June 2, with the last confirmed case of shigellosis on May 15 and the food handler no longer a carrier of the organism, the GHD lifted all measures instituted with the Health Order issued on May 5.

Discussion

An epidemiological investigation of the food handler revealed that in late March, two of her child's friends returned from Mexico during spring break exhibiting diarrhea. These children had been at her home during a portion of their illness. It is believed that these children were the original source contacts and that the food handler was communicable, although asymptomatic, throughout the episode.

An asymptomatic food handler would explain the occurrence of shigellosis in children grouped in separate classrooms and the length of time between cases. The food handler was a certified food service manager, registered with GHD.

As this outbreak demonstrates, good personal hygiene and hand washing techniques by all food preparers are of paramount importance, but the day care environment is very conducive to diarrheal diseases. It is estimated that 11.4 million children spend at least 10 hours per week in the institutional day care environment (5).

Close contact of children too young to practice good hand hygiene results in the attack rate of diarrheal diseases to be the highest in the age group of children less than three years of age. Studies have found that nearly one-third of the Shigella cases investigated in the day care environment also resulted in secondary cases in their families (5).

Outbreaks of Shigella sonnei and other diarrheal diseases can be prevented by implementing some rudimentary isolation procedures. One tactic is to place children into small groups. These groups should be separated for all activities, such as play and lunch. Separate toilet-trained children from those that are not. Research has shown over a three-and-one-half times higher attack rate of diarrheal diseases in centers that accepted children less than two years of age (5).

A simple daily "health screening" at the entrance of the center for each child will alert the care givers to potential problems. Children are often contagious before they look or act sick. For this reason, attention must be given to all aspects of hygiene and sanitation.

Children and employees must be taught the importance of good hygiene and proper hand washing. Hands should be washed before preparation, service or consumption of food or medications; after play or activity time; after changing a diaper and after toilet use or after helping a child use the toilet.

A common method of spreading an infectious diarrheal disease is changing a diaper. The first rule is that the diapering table should not be in the food preparation or eating area. Along with this, the food server should never diaper or toilet children. Studies have shown a three-fold increase in the attack rate of diarrhea in centers that combine duties (5). Diaper changing must be done properly during each change to adequately protect the child and the care giver:

* use disposable gloves

* remove soiled diaper and clothing carefully

* clean with disposable towelettes

* throw diaper, towelette and gloves in plastic bag and place in lined step can

* rediaper and dress

* wash child's hands

* clean and sanitize diaper station (100 ppm chlorine solution in a properly labeled bottle)

* properly wash hands (hand sink must be convenient to changing station)

An ill child policy must be developed in each day care center. Separate a sick child from healthy children and from other sick children. Assign one staff member to the ill child and never move staff from sick children to healthy children. Diaper ill children apart from healthy ones.

Another important way to prevent the spread of infectious diseases is to routinely and regularly clean and sanitize the facility. Sullivan, et al. studied cleaning in the day care environment. Their survey found that 89 percent of the studied centers sanitized their diaper-change area after each use; 95 percent sanitized their bathrooms daily; 74 percent sanitized their floors daily; 69 percent sanitized their play areas daily; and only 16 percent sanitized their toys daily (5,6).

Toys used by children in diapers must be sanitized between uses. All toys should be sanitized daily by the use of the three step method of washing in detergent, rinsing with water, sanitizing and allowing to air dry. Treat stuffed animals as personal items that belong to one child only.

Mats, cots and bed linens must be individually marked and matched to one child. Sanitize mats at least once a week. Provide separate locker areas for each child.

Toilet rooms should be cleaned and sanitized daily. Koopman reported 44 percent of cases in a Shigella outbreak to have been spread by contaminated toilet surfaces (5, 7). All areas of the center should be sanitized at least once a week. Vacuum carpeted areas daily. Carpeted floors in toddler rooms should be avoided because of the inability to properly sanitize such surfaces.

These sanitation procedures, once implemented, must be augmented with proper employee training and thorough supervision. The hygiene and sanitation program must become a habit, practiced by all, to eliminate potential situations which could enhance an infectious diarrheal disease outbreak.

The regulatory agency responsible for assuring compliance with sanitation guidelines must equitably enforce statutes while continually educating and suggesting additional methods of preventing disease outbreaks. All responsible parties must be aware that one case of an infectious disease in an institutional setting can rapidly become an uncontrolled outbreak.

The GHD has confronted two other Shigella sonnei incidents in licensed day care centers since the documented cases in April/May 1992. In both of these recent incidents, the GHD notified parents and instituted hygiene requirements after notification of the first ill child. A secondary case was never documented in either incident.

The diarrheal disease outbreak control procedure practiced by the GHD appears to be effective. Upon notification of a single case of shigellosis in a licensed day care center the following actions are implemented:

* Immediately visit and inform the day care center.

* Issue a Health Bulletin to all parents of children enrolled in the center. The Bulletin explains the disease, its transmission and control methods. The public health importance of not moving a child from the infected center is also discussed.

* Issue a notice to all staff members requiring them to observe strict hand washing techniques. The notice also requires children's hands to be washed following toilet usage, after play time and before eating.

* Require thorough sanitization of all surfaces in the day care center. Particular attention must be paid to the diaper changing stations, toilet rooms and toys used by toddlers or infants.

The investigated shigellosis cases, although not life threatening, were a tremendous inconvenience for the patients and for their families, and were very costly in time and treatments for everyone involved. Good hand hygiene practiced by the children and the day care staff accompanied by the documented sanitation techniques, albeit laborious, will reduce or eliminate infectious diarrheal diseases and thus save the children, their parents, and the care givers the aggravation associated with a Shigella sonnei outbreak.

References

1. Joklik, W.K., H.P. Willett and D.B. Amos (eds.) (1980), Zinsser Microbiology, 17th ed., Appleton-Century-Crofts, New York, NY.

2. Benenson, A.S. (ed.) (1990), Control of Communicable Diseases in Man, American Public Health Assoc., Washington, D.C.

3. Wehrle, P.F. and F.H. Top, Sr. (eds.) (1981), Communicable and Infectious Diseases, 9th ed., The C.V. Mosby Company, St. Louis, MO.

4. Boyd, R.F. and B.G. Hoerl (1981), Basic Medical Microbiology, Little, Brown and Co., Boston, MA.

5. Osterholm, M.T., J.O. Klein, S.S. Aronson and L.K. Pickering (eds.) (1987), Infectious Diseases in Child Day Care, The Univ. of Chicago Press, Chicago, IL.

6. Sullivan, P., W.E. Woodward, L.K. Pickering and H.L. DuPont (1984), Longitudinal study of diarrheal disease in day care centers, Am. J. Public Health 74:987-991.

7. Koopman, J.S. (1978), diarrhea and school toilet hygiene in Cali, Colombia, Am. J. Epid. 107:412-420.

Richard T. Briley, M.S., R.S., Garland Health Dept., P.O. Box 469002, Garland, TX 75046-9002.