The use of a mobile laboratory unit in support of patient management and epidemiological surveillance during the 2005 Marburg Outbreak in Angola

Abstract

Background: Marburg virus (MARV), a zoonotic pathogen causing severe hemorrhagic fever in man, has emerged in Angola resulting in the largest outbreak of Marburg hemorrhagic fever (MHF) with the highest case fatality rate to date.

Methodology/principal findings: A mobile laboratory unit (MLU) was deployed as part of the World Health Organization outbreak response. Utilizing quantitative real-time PCR assays, this laboratory provided specific MARV diagnostics in Uige, the epicentre of the outbreak. The MLU operated over a period of 88 days and tested 620 specimens from 388 individuals. Specimens included mainly oral swabs and EDTA blood. Following establishing on site, the MLU operation allowed a diagnostic response in <4 hours from sample receiving. Most cases were found among females in the child-bearing age and in children less than five years of age. The outbreak had a high number of paediatric cases and breastfeeding may have been a factor in MARV transmission as indicated by the epidemiology and MARV positive breast milk specimens. Oral swabs were a useful alternative specimen source to whole blood/serum allowing testing of patients in circumstances of resistance to invasive procedures but limited diagnostic testing to molecular approaches. There was a high concordance in test results between the MLU and the reference laboratory in Luanda operated by the US Centers for Disease Control and Prevention.

Conclusions/significance: The MLU was an important outbreak response asset providing support in patient management and epidemiological surveillance. Field laboratory capacity should be expanded and made an essential part of any future outbreak investigation.

Figure 1. Laboratory set up and procedures.

Laboratory space was made available to us in the Paediatric Ward of the Uige Provincial Hospital. Four rooms were used for the laboratory set up to ensure isolation of infectious work from other activities and to separate PCR assay steps to minimize contamination. (A) Room for RT-PCR master mix preparation; (B) room for sample inactivation; (C) room for RNA extraction and real-time RT-PCR; (D) room for PPE donning and disinfection.

Figure 2. Diagnostic algorithm.

Key: pos  =  positive; neg  =  negative.

Figure 3. Field MARV diagnostic lab at Uige, Angola 2005; daily case load and positive sample detection.

The height of each bar represents the total daily case load for the lab with the positive cases indicated by the solid portion.

Figure 4. Age and gender distribution of positive cases.

Positive cases identified during the operation of the field lab are shown separated by age and gender (female ▪ and male □). The distribution of positive cases demonstrates a higher proportion of females (68%) and children, 0 to 5 years, (21%) among the infected individuals.

Figure 5. Cycle threshold values for paired blood and swab samples.

Cases where whole blood (▪) and swab (□) samples were available for testing the same day are shown. Viral loads from both sample sources were comparable and do not consistently indicate one sample source as more suitable for viral load determination.