Outbreak of Adenovirus Acute Respiratory Disease in Aseer, Southern Saudi Arabia, April 2001

In April 2001, in a school compound at Al Ergeen center, Sarat Abeedah, Aseer region, southern Saudi Arabia, a large number of male students reported headache, fever, cough, sore throat, rhinitis and gastrointestinal disturbance. The same symptoms appeared a few days later among students in a female school compound. A team from the Field Epidemiology Training Program (FETP), in collaboration with the local health authorities investigated this outbreak.

A descriptive cross sectional study was conducted, where all students and staff in both school compounds were interviewed. On the next day, residences of the cases were visited and the patients admitted into the hospital were also interviewed.. A case was defined as any person in Al Ergeen area who had fever, headache, cough, myalgia, rhinitis in the outbreak area, with or without gastrointestinal symptoms (nausea, vomiting, diarrhea), within the period from 15/4/2001 to 7/5/2001. Since most cases had occurred after a recent change in water supply of the boys school, a waterborne cause of the outbreak was suspected. Water supply to each school and to houses in the district was thoroughly investigated.

A total of 622 individuals were included in the study; 312 males (50.2%) and 310 females (49.8%). The major constituent of the sample was students i.e. 576 (92.6%), in addition to 33 (5.3%) teachers, and 13 (2%) administrative and other personnel. Among males the median age was 16 years (range 2-55 years), and Saudis represented 97.8%. The median age for females was 13 years (range 4-43 years), and Saudis represented 99.4% of the total females.

The number of individuals who met the case definition was 156, representing 25.1% of the total population studied, among those 71.8% were males and 28.2% were females. The age group most affected was 16-20 years. The common symptoms were headache (54.2%), cough (50.5%), fever (49.2%), and rhinitis (40.8%). Males were 3.39 times at higher risk of acquiring the disease than females. No serious cases or complications were reported. Only 19 cases were admitted to the hospital and were discharged within a couple of days without any serious complications.

The epidemic curve (Figure 1) indicates a person-to-person transmission of infection with a sequential gender spread, males followed by females. The spread of infection from male to female school compounds could have happened as a result of disease transmission among family members in the household environment. Laboratory investigations confirmed that the causative organism of the infection was Adenovirus (Adenovirus IgM ELISA).

On the basis of available local information, the initial impression of the community and investigators was a common source outbreak, and recently changed water source was suggested to be the cause of outbreak. The water source for the male school had been a nearby well, which had been switched to Almashrou for reconstruction purposes. Suspicion was directed towards Legionnaires disease, which has similar clinical features and is known to affect populations with the same water supply.

Legionnaire's disease is caused by a gram-negative bacilli, that grows in water over 25°C in temperature, and spreads by an aerosol route[1] Males are affected twice as commonly as females, and the incubation period is 2 €“ 10 days. The characteristic picture of the disease is malaise, myalgia, headache, and fever. Half of the patients usually have gastrointestinal symptoms. A recognized epidemiological pattern of the disease has been observed in outbreaks among previously fit individuals staying in hotels, institutions or hospitals where shower facilities or cooling systems had been contaminated with the organism. [1,2]

Laboratory investigations, however, confirmed that the causative organism was Adenovirus, which are human pathogens that commonly infect the respiratory and gastrointestinal tracts. [3] Adenovirus infections are endemic, particularly among children, but may also cause epidemics of pharyngoconjunctival fever, keratoconjunctivitis, gastroenteritis, and acute respiratory disease. About 4 to 5% of clinically recognized respiratory illnesses in civilian populations are caused by adenoviruses.[4] Person-to-person transmission is presumably the principal mechanism of spread of infection, along with fecal-oral, and occasionally waterborne transmission.[4] The incubation period is between 3 to 10 days, with illness lasting 1 week or over. Diarrhea is more prominent than vomiting or fever, and respiratory symptoms are often present.[5]

Although the epidemiological investigative team were initially influenced towards the assumption of a water-related disease, this assumption changed after investigating the outbreak in more detail, putting in consideration that the water sources supplied all the schools and houses in the region, whereas cases appeared in certain confined places (school compounds); different water dealers supplied the male and female school compounds; the onset of symptoms preceded the change in water supply in some cases; and the epidemic curve did not support the common source pattern of disease occurrence. The clinical picture of respiratory and gastrointestinal symptoms was suggestive of a viral infection, which affected the respiratory and gastrointestinal tracts, the symptoms of which spread fast in an overcrowded population in both schools. This assumption was supported by the presence of 3 peaks in the epidemic curve, suggesting person to person spread of infection. Laboratory investigation confirmed the diagnosis of adenovirus infection.

This investigation highlights that during an outbreak investigation, focus should not be on the most obvious suspected exposure alone, rather, the whole epidemiological picture should be looked into methodically.