Chickenpox Outbreak Among Laborers In A Company Compound North Of Riyadh, 2001, Saudi Arabia

On Friday August 10th, 2001, a notification from the Saudi Red Crescent to Riyadh Regional Health affairs reported cases of an unknown disease among laborers in a company compound north of Riyadh. The Field Epidemiology Training Program (FETP) was assigned to investigate this outbreak. Primary inspection identified 23 male patients complaining of fever and rashes all over their body of different durations, among a total of 350 laborers living in the compound. Twenty-three cases of chickenpox were identified, four were confirmed by laboratory. Investigation aimed to determine the size of the problem, possible cause of the outbreak, and development of measures to prevent similar situations in the future.

A case control study was conducted, a case was defined as any person from this company compound with rash, fever or blisters in his body, from 13/7/2001 to 22/8/2001. A list of laborers names was provided by the company, from which we randomly selected healthy individuals living at the same compound to be controls. A standard questionnaire was developed. All cases and controls were interviewed face to face by the help of translators provided by the company. Information collected included demographic information, duration of being in Saudi Arabia, whether he spent his vacation at his home country and date of arrival from vacation, history of direct contact with a chickenpox case or a person who developed symptoms of chickenpox, personal hygiene measures, and past history of chickenpox. Crowding at the camp was also investigated.

A total of 23 cases and 78 controls were interviewed, all were male laborers from Bangladesh. The mean age of cases was 26 ± 6 (range 18-38) years. Those who did not have previous history of chickenpox had 16 times the risk of infection than those who did (0.R=16, P-value=0.0008), which was the main risk factor. Exchanging clothes between laborers played a very important role in transmission of the disease (AR=50%, OR= 4.5, p-value= 0,006), in addition to contact with a diseased individual (AR-65%, OR=3.6, p-value= 0.014).

The compound was composed of four one-floor buildings. Three of these buildings were composed of 20 rooms, four toilets, four bathing areas, and two kitchens. Each room size was 2 x 3.5 m2, with one window (1 m2) that was always closed. The air-conditioning was not working efficiently. The fourth building was divided into a mosque and two rooms. Each room in the compound was shared by 6 laborers.

The first case appeared on 18/7/2001, and might have been the index case and source of the outbreak. The second case appeared on 23/7/2001. The number of cases increased because of the high density of individuals in small rooms and non-proper isolation of the patients. The peak of the outbreak was recorded on 1/8/2001. Until the 10th of August 2001 all patients had been isolated in the compound, where they were still able to contact unaffected individuals and share the same facilities. Proper preventive measures were taken on 10/8/2001, when the company arranged a separate isolation flat for the patients. The epidemic curve (Figure I) represents the spread of the disease and the effect of proper isolation. All cases had identical signs and symptoms of chickenpox, however none of our study patients developed any symptoms of respiratory infection or other complication and none needed to be admitted into hospital.

Chickenpox is a highly contagious viral illness caused by Varicella zoster virus, with secondary attack rates in susceptible house-hold contacts of up to 90%.[1-3] Its incubation period may be as short as 7 days or prolonged up to 21 days in a normal individual. The period of communicability extends from one to two days before the onset of rash through the first five to six days after rash.

Chickenpox is a childhood disease in non-tropical countries, where children between the age of five and nine are most commonly affected, accounting for 50% of all cases. Ten percent of cases are seen in young adults where complications tend to be more serious.[1-2] There are no race or sex differences in either susceptibility to, or expression of, the disease.[2] In most cases the older the child, the more severe the attack.[1] However, the epidemiology of chickenpox in tropical regions is different than that of temperate areas, and is poorly understood. Varicella infection appears to be more common among adults living in the tropics than among those living in temperate areas, suggesting that there is decreased transmission in younger age groups. The reasons for this difference in the age-specific epidemiology of Varicella, including the possible roles of population size, population density, crowding, and higher ambient temperatures in the tropics, are not clear.[4]

Humans are the reservoir of Varicella zoster. It can be transmitted from person to person by direct contact, droplet, and airborne spread of secretions from the respiratory tract of cases or from the vesicle fluid of patients. In case of direct contact, infection occurs through articles freshly soiled by discharge from vesicles of infected persons.[1,4]

In this outbreak, it is noted that all the patients were adults, living in a high-density compound and were all having the first attack of chickenpox. Chickenpox infection, therefore, is not restricted to a specific age if the person is not immune. However, Chickenpox infection in adults is more severe and has a higher risk of complications than in children.[1,4] Although less than 2% of reported cases are in persons under 20 years of age, this accounts for approximately 25% of mortality. The case fatality rate in children is approximately 1/100,000; in infants approximately 6/100,000 and in adults is approximately 12/100,000. The majority of deaths occur in normal individuals (children and non-immunocompromised).[4,5] The study result was similar to other studies reporting susceptibility of infection among a non-immunized population. Epidemics usually occur in such gathering accommodations and camps, especially among those who have not been exposed to pediatric disease, which makes them more susceptible. Absence of immunity among the laborers was the main risk factor for acquiring the infection. However, late isolation and low hygienic standards helped in dissemination of the disease among the closed and highly crowded population.

Laborers were educated on the importance of personal hygiene. Physicians working at accommodation compounds should apply accurate prevention measures to prevent spread of contagious diseases if they occur. Isolation should always be established as the first prevention measure. Companies should be instructed on the number of the laborers that should occupy each room with the improvement of ventilation. Those living in camps i.e. laborers, students, soldiers, should be re-immunized.