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THE NZARA OUTBREAK OF VIRAL HAEMORRHAGIC FEVER

D.H. SMITH (1), D.P. FRANCIS (2), D.I.H. SIMPSON (3), R.B. HIGHTON (4)
1. Tana Project, Ministry of Health, P.O. Box 53131, Nairobi, Kenya.
2. Center for Disease Control, Atlanta, U.S.A. 3. London School of Hygiene and Tropical Medicine, England. 4. Medical Research Council, Malindi, Kenya.

The detailed epidemiology of African Haemorrhagic Fever in the Southern Sudan has been dealt with by Francis (this report). This brief account is intended to supplement this with some details of the Nzara outbreak especially where differences were observed. The investigation in Nzara was carried out retrospectively and, as it appeared probable that Nzara was the original focus of the disease in the Sudan, particular attention was paid to the possible routes of introduction of the disease into the human population.

THE AREA OF THE OUTBREAK

Nzara is a township in Yambio District, Western Equatoria, of some 20,000 people clustered around an extensive agricultural organization and Cotton Manufacturing Factory employing a total of 2,000 staff. The town is partly composed of brick built houses in labour lines and surrounded by densely inhabited areas with mud and thatched tukals, housing the majority of the town's population.

Ecologically, the area lies close to the central African rain forst zone. It is rich agricultural country with extensive teak plantations and fruit orchards. Much of the area is dense woodland with areas of secondary forest. The civil disturbances of the last two decades had caused many people to leave the area, but since the early 70's the area has become rapidly repopulated with subsequent reclamation of forested areas for subsistence farming as population pressure increases.

THE ORIGIN OF THE OUTBREAK

The original cases of haemorrhagic fever occurred amongst employees of the Nzara Cotton Factory; the first case (YuG) fell sick on June 27th and died in hospital on July 6th after an illness lasting for nine days. Both the hospital records and descriptions obtained from close relatives described an illness with features indistinguishable from those of subsequent cases. During his illness he was nursed in hospital by his brother (YaG) who fell sick one week after the death but survived. Examination of serum from the family contacts and also the surviving brother were negative. They lived some six miles out of Nzara on the old Maridi road. This first case had been a store keeper working in the cloth room of the Cotton Factory.

The second case (Bz) who died on July 14th, also in hospital, worked in the cloth room of the Cotton Factory. Following his death his wife, his only surviving relative, also died. Both were reported as having suffered a severe haemorrhagic illness.

The third and most important case in Nzara (PG) worked alongside these previous two males in the cloth room in the Cotton Factory. He fell sick on July 18th and after several short stays in the hospital died on July 27th. He lived approximately one mile south of the Cotton Factory in a densely populated area.

These three men working in the Cotton Factory had remarkably little social contact; they lived in quite separate areas around the township and behaved in quite different manners. The first two cases were described as quiet unremarkable people whilst the third case (PG) was involved in a variety of enterprises within the town. His home was next to a shop run by a merchant (MA). He helped in the shop acting as an interpreter for visiting tradesmen, including those from Zaire and often ate with the family. Two brothers staying in the household were close personal friends of his. They were involved with a local jazzband and in addition PG has a number of close girl friends. Following his illness and eventual death, there was an eruption of cases involving the MA household, the family of their servant and six women who had closely attended him whilst sick. From this single case 69% of all Nzara cases and 87% of deaths could be traced. Also from this the MA family provided the first introduction of cases to Maridi and Tembura and very possibly the route of introduction to Zaire through lorry drivers who stayed in the household and travelled between Northern Zaire and Western Equatoria for the purpose of trading in beer, cigarettes and light machinery. Thus the majority of cases occurring in the Nzara area were traced to this single infection. Direct man to man transmission was subsequently observed through six generations of cases.

OTHER CASES IN NZARA

In addition to this predominant cluster of cases a series of other cases occurred in Nzara township between July and early October 1976 in which no direct contact could be established with previous cases. This aspect of the epidemiology appears quite distinct from the pattern observed in Maridi.

Of these apparent primary cases three worked in the cloth room at the Cotton Factory; two in the adjacent weaving section; one in maintenance and two were agricultural officers employed by the corporation. In only one of these cases (AR) whose onset of disease was in mid September was there any evidence of positive serology despite the fact that six survived their infections.

THE COTTON FACTORY

Apart from the two agricultural employees both living to the south of Nzara, the main focus of infection appeared to be the Cotton Factory; predominantly the area around the cloth room and weaving sections. Presumably, either transmission was occurring direct from person to person following its original introduction into this population and behaving quite unlike the subsequent epidemiology pattern observed both in Nzara and Maridi or alternatively transmission was being effected within the factory from an animal source.

The Cotton section of the Factory employs some 480 staff. Another 500 also worked in surrounding buildings concerned with the manufacture of cotton seed cake, cotton seed oil and soap. The Cotton Factory is housed in a single large building divided into various sections. Raw cotton is taken in at one end and is processed within the same building to the finished cloth. The cloth room and store are adjacent to the weaving section at one end of the building and employed 24 staff. From this one area 4 deaths (16%) occurred and a further 5 cases were seropositive in November. Thus, 37% would appear to have been exposed to infection in sharp contrast to the remainder of the factory staff (Table 1). These findings are also in sharp contrast to the serology both of suspect cases, in whom only 16% were positive, and close family contacts in whom only 2% were positive. In a follow up survey of all cases found to be seropositive in the factory in November 1977, half of these cases gave no history of previous illness over the preceding 12 months whilst the other 50% gave history only of a minor febrile episode.

Examination of the cotton factory showed that rat infection was especially prevalent and in addition the roof housed considerable populations of bats. There was no evidence that there had been any recognizable epizootic in either of these populations. Limited numbers of both rats and bats were collected for virological studies and the results are awaited with considerable interest.

The Cotton Factory also has a small clinic room where minor illness in the factory employees are treated. The clinic is run on a daily basis by a nurse employed by the corporation. She treats predominantly minor illnesses and injuries. Injections of chloroquire and occasionally antibiotics are given in this dispensary.

A definite history of previous injection was not obtained in any of the surviving cases detected clinically during the survey.

TABLE I
SEROLOGICAL SAMPLING IN VARIOUS GROUPS IN NZARA


Group


No collected


+ve


%


1. Probable cases


27


4


16


Possible cases


10


2


20


Total


37


6


16


2. Close household contacts


41


1


3


3. Immediate neighbours


18


0


-

4. Cluster samples


around the home of YuG


19


0


-


5. Employees of the Cotton Factory:

     

Weaving room


55


2


4


Spinning room


28


1


4


Cloth room


17


3


18


Drawing in room


9


1


11


Of the Cotton Factory employees found seropositive in November, approximately 50% would have had injections at the dispensary for their minor febrile illnesses. A careful enquiry revealed no evidence of co-primary cases occurring related to syringe passage.

The high proportion of seropositivity amongst the Cotton room employees in sharp contrast to the low prevalence of antibodies both in clinically suspect cases and in close contacts of known cases and deaths is strongly suggestive of continued transmission within the Cotton Factory, beyond the period of the epidemic occurring in Nzara. The contrast in serological results in Maridi and Nzara plus the decline observed in antibodies titres between November and January would appear to suggest that demonstrable antibody responses are a rather transient phenomenon.

If this is so, then it would support the view that those cases found seropositive in the Cotton Factory had been infected more recently than cases occurring in the township and discovered during epidemiological surveillance.

The available evidence suggests that the Cotton Factory was the predominant source of infection and that a series of apparently primary cases occurred in this population. In most cases whilst in the one notorious, incident of case three (PG) the infection appeared to lead to at least six generations of cases in Nzara alone. The question of syringe passage with regard to transmission from this case must also be considered. Two nurses were involved in this outbreak and both died. They visited patients, including the original case (PG) in their home and were known to have given injections. It is quite conceivable that the friends and neighbours of this case might have received prophylactic injections at the time of the original illness or subsequence to his death.

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