Measles outbreak in South Africa: epidemiology of laboratory-confirmed measles cases and assessment of intervention, 2009-2011

BACKGROUND: Since 1995, measles vaccination at nine and 18 months has been routine in South Africa; however, coverage seldom reached .95%. We describe the epidemiology of laboratory-confirmed measles case-patients and assess the impact of the nationwide mass vaccination campaign during the 2009 to 2011 measles outbreak in South Africa. METHODS: Serum specimens collected from patients with suspected-measles were tested for measles-specific IgM antibodies using an enzyme-linked immunosorbent assay and genotypes of a subset were determined. To estimate the impact of the nationwide mass vaccination campaign, we compared incidence in the seven months pre- (1 September 2009–11 April 2010) and seven months post-vaccination campaign (24 May 2010–31 December 2010) periods in seven provinces of South Africa. RESULTS: A total of 18,431 laboratory-confirmed measles case-patients were reported from all nine provinces of South Africa (cumulative incidence 37 per 100,000 population). The highest cumulative incidence per 100,000 population was in children aged ,1 year (603), distributed as follows: ,6 months (302/100,000), 6 to 8 months (1083/100,000) and 9 to 11 months (724/100,000). Forty eight percent of case-patients were $5 years (cumulative incidence 54/100,000). Cumulative incidence decreased with increasing age to 2/100,000 in persons$40 years. A single strain of measles virus (genotype B3) circulated throughout the outbreak. Prior to the vaccination campaign, cumulative incidence in the targeted vs. non-targeted age group was 5.9-fold higher, decreasing to 1.7 fold following the campaign (P,0.001) and an estimated 1,380 laboratoryconfirmed measles case-patients were prevented. CONCLUSION: We observed a reduction in measles incidence following the nationwide mass vaccination campaign even though it was conducted approximately one year after the outbreak started. A booster dose at school entry may be of value given the high incidence in persons .5 years.Our acknowledgements go to the Department of Health South Africa, National, provincial and districts, the South African Field Epidemiology and Laboratory Training Programme (SAFELTP), for ongoing support in surveillance and outbreak activities; Division of Epidemiology (Tsakani Nkuna, Kelebogile Lebogang Motsepe) and Virology (Londiwe Mahlaba, Mduduzi Buthelezi, Nomfundo Radebe, Muzi Hlanzi, Wayne Howard) at the NICD-NHLS for data management and laboratory testing support respectively and Private Laboratories for their support and referring specimens to the NICD.www.plosone.orgam201

Age-specific incidence of laboratory-confirmed measles cases, South Africa, 2009–2011.

<p>Age-specific incidence of laboratory-confirmed measles cases, South Africa, 2009–2011.</p

Weekly* number of measles IgM positive cases: South Africa, 2009–2011.

<p>* Week calculated from date of specimen collection (n = 17 351), date received (n = 1 067) or date tested (n = 13).</p

Reported administrative vaccination coverage^* by province during the nationwide mass vaccination campaign, South Africa, May/April 2010.

*<p>Administrative method: number of doses delivered divided by the target population which is determined from the census projections.</p><p>mo = months; yr = years.</p>**<p>8 of 9 provinces of South Africa included, Gauteng Province excluded as widespread vaccination was conducted in this province in 2009.</p><p>Source: Personal Communication: National Department of Health, South Africa.</p

Characteristics of laboratory-confirmed measles cases before and after the vaccination campaign in seven South African provinces, 2009–2010.

*<p>Age and sex known in 6,729 and 6,866 cases respectively; <b>#</b> Age and sex known in 1,291 and 1,319 cases respectively; mo = months; yr = years.</p><p>Please note: population for the <1 year unavailable per month; as a result, the population was estimated by dividing the population of <1 year by 12.</p

Map showing nine South African provinces and overall cumulative incidence per 100 000 population by province, 2009–2011.

<p>Map showing nine South African provinces and overall cumulative incidence per 100 000 population by province, 2009–2011.</p