Njeru et al. BMC Infectious Diseases (2015) 15:245
DOI 10.1186/s12879-015-0989-6
RESEARCH ARTICLE
Open Access
Rubella outbreak in a Rural Kenyan District,
2014: documenting the need for routine
rubella immunization in Kenya
Ian Njeru1*, Dickens Onyango1, Yusuf Ajack1 and Elizabeth Kiptoo2
Abstract
Background: Rubella infection has been identified as a leading cause of birth defects commonly known as
Congenital Rubella Syndrome (CRS). Kenya does not currently have a rubella immunization program nor a CRS
surveillance system. In 2014, a rubella outbreak was reported in a rural district in Kenya. We investigated the
outbreak to determine its magnitude and describe the outbreak in time, place and person. We also analyzed the
laboratory-confirmed rubella cases from 2010 to 2014 to understand the burden of the disease in the country.
Methods: The Rubella outbreak was detected using the case-based measles surveillance system. A suspected case
was a person with generalized rash and fever while a confirmed case was a person who tested positive for rubella
IgM. All laboratory-confirmed and epidemiologically linked cases were line listed. The measles case-based surveillance
database was used to identify rubella cases from 2010 to 2014.
Results: A total of 125 rubella cases were line listed. Fifty four percent of cases were female. Case age ranged from
3 months to 32 years with a median of 4 years. Fifty-one percent were aged less than 5 years, while 82 % were aged
less than 10 years. Six percent of the cases were women of reproductive age. All cases were treated as outpatients
and there were no deaths. The number of confirmed rubella cases was 473 in 2010, 604 in 2011, 300 in 2012, 336 in
2013 and 646 in 2014.
Conclusions: Analysis of Kenya rubella data shows that rubella is endemic throughout the country, and many
outbreaks may be underestimated or undocumented. Six percent of all the cases in this outbreak were women of
reproductive age indicating that the threat of CRS is real. The country should consider initiating a CRS surveillance
system to quantify the burden with the goal of introducing rubella vaccine in the future.
Keywords: Rubella, Outbreak, Congenital Rubella Syndrome
Background
The prevention of birth defects has been identified as
global health priority [1]. Birth defects or congenital
anomalies are a significant cause of morbidity, disability
and mortality in many countries [2–5]. Rubella infection
has been identified as one of the leading causes of birth
defects globally [1].
Rubella, sometimes called German measles or threeday measles, is a contagious viral disease. The infection
is usually mild with fever and rash. However, maternal
infection during the first trimester of pregnancy can
* Correspondence: iannjeru75@yahoo.com
1
Disease Surveillance and Response Unit, Ministry of Health, Nairobi, Kenya
Full list of author information is available at the end of the article
cause serious congenital malformations in the fetus, a
condition which is known as Congenital Rubella Syndrome (CRS) [6].
The annual incidence of CRS in developing countries
is estimated to be 110,000 cases per year, with a range
of 14,000–308,000 [7]. The most common manifestation
of CRS is deafness. Eye defects including glaucoma and
retinopathy are common, and heart defects can also
occur [8, 9].
The rubella vaccine contains a live attenuated (weakened) virus; immunization with two doses is highly effective to prevent rubella [10, 11]. The ultimate goal of
rubella vaccination is to prevent the occurrence of CRS
[12]. The World Health Organization (WHO) currently
© 2015 Njeru et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License
(http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium,
provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://
creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Njeru et al. BMC Infectious Diseases (2015) 15:245
advocates for the use of rubella-containing vaccines (RCVs).
RCVs are administered in monovalent form (rubella only)
or in combinations such as Measles-Rubella (MR) or
Measles-Mumps-Rubella (MMR) [13]. By December 2009,
130 WHO member states including two of 46 WHO Africa
region member states used RCVs within their routine
immunization systems [14].
Rubella vaccine is widely available through routine
immunization programs in developed countries. However
is it is not available in many developing countries including Kenya [15]. National rubella immunization programs
in the developed countries utilize one of the following
strategies: selective immunization of women, vaccination
of infants, or a combined strategy [16]. When an infant
vaccination strategy is adopted, there is need for sustained
high coverage so as to ensure the susceptibility of adult
women is not increased [17]. Although any of the three
strategies could be used, it is important to include the
vaccination of women of childbearing age [18, 19]. The
vaccine is delivered through routine immunization or
Supplemental Immunization Activities.
Rubella surveillance in Kenya is integrated within the
national case-based measles surveillance system. Through
this system, approximately 400 rubella cases are confirmed annually [20]. There is poor understanding of the
burden of rubella infection and its prevalence among
pregnant women in Kenya. A few studies have sought to
establish the burden of rubella in Kenya. These studies,
two in pregnant women and one in children were conducted in diverse parts of the country [20–22]. The study
in pre-primary and primary school children identified
an overall rubella sero-positivity of 80 %, with the
highest sero-positivity (94 %) detected among children
aged 14–20 years [20]. The studies in pregnant women
showed that approximately 7 % were susceptible to rubella infection [21, 22].
Although rubella cases are detected every year through
the measles surveillance system, a rubella outbreak in
Kenya has not previously been described in the published
literature. In 2014, a rubella outbreak was reported in
Njoro, a rural District in Rift Valley Region of Kenya. We
investigated the outbreak to determine its magnitude and
describe the outbreak in time, place and person. We also
analyzed laboratory confirmed rubella cases in the last
5 years (2010–2014) in order to fully define the burden
of the disease in the country.
Methods
Study site
The study was conducted in Njoro district, located in
Nakuru County, 150 km West of Nairobi (the capital
city of Kenya). Njoro district is one of the nine districts
in Nakuru County and has a population of 184,859.
Page 2 of 6
Study design
We did a retrospective analysis of data collected during
the outbreak which occurred from March to May 2014.
Laboratory investigations
Cases were identified through the measles case-based
surveillance system which is also a passive surveillance
system for rubella. Attending clinicians identified cases
of fever and macula-papular rash during triage. Those
who met the suspect case definition were notified to the
district surveillance officer who completed a case-based
surveillance form. The case-based surveillance form was
sent to the national level of the Ministry of Health, while
a copy was submitted to the laboratory with the blood
specimen. Blood specimens were collected from the
first six suspected cases. All six specimens were initially
tested for measles-specific immunoglobulin M (IgM) antibody using a standard enzyme-linked immunosorbent
assay (ELISA). All six specimens were negative for measles
IgM, thus, they were tested for rubella-specific IgM antibody using ELISA. The laboratory testing was performed
at Kenya Medical Research Institute (KEMRI) laboratory
which is accredited by the WHO.
Case definition
A suspected case of rubella was defined as anyone who
presented with fever and maculo-papular rash from
Njoro District from 1st March 2014 to 15th May 2014. A
confirmed case was one that tested positive for rubella
IgM. A probable case was one that had close contact
with another case. As was the routine with measles and
rubella surveillance in the country, once 5 or more samples from one district were laboratory-confirmed, it was
no longer considered necessary to test all the samples.
Therefore, all subsequent cases that presented with
fever and maculo-papular rash were line-listed as rubella cases, provided they were epidemiologically linked
to another case. An epidemiological link was defined as
having been in close contact with someone with similar
symptoms within the last 3 weeks. Close contact was defined as someone who lived in the same household,
attended the same school or played together with the case.
Data collection and analysis
Rubella cases were entered into an Excel line list during
the outbreak. The line list captured socio-demographic
variables including name, age, sex, date of onset, date
seen at the facility, residence, laboratory results and outcome of illness. Information on measles and rubella vaccination status for each case was also collected. Data
analysis was done using Epi Info version 7.
The study was approved by the Ministry of Health as
part of routine surveillance and outbreak investigations
Njeru et al. BMC Infectious Diseases (2015) 15:245
Page 3 of 6
Fig. 1 Epicurve of Rubella outbreak, Njoro District, Kenya, 2014
and was therefore exempted from ethical committee
review.
Results
All 6 samples taken for laboratory confirmation on the
first day of the outbreak (18th March 2014) tested
positive for rubella IgM. Subsequently, a total of 125
rubella cases were line listed. The index case for this
outbreak was believed to be a 2 year old child who
accompanied his parents to another district that had
reported laboratory- confirmed rubella cases, and returned to his home district on 1st March 2014. This
child developed fever and rash on 2nd March 2014.
Although the index case was not laboratory-confirmed,
two cases developed rashes after contact with him, and
were subsequently laboratory-confirmed. The peak of the
outbreak occurred on 20th March 2014 while 38 % of all
cases occurred in the first 3 days of the outbreak. This
was followed by a gradual decline but with several
intermittent smaller peaks. The last case occurred on
5th May 2014 (Fig. 1).
Fifty four percent of all cases were female with the age
ranging from 3 months to 32 years with a median of
4 years. Fifty one percent of the cases were aged less
than 5 years while 82 % were aged less than 10 years. A
total of 7 cases (6 % of all cases) occurred in women of
reproductive age (15 to 49 years) (Fig. 2). The outbreak
started in one village but quickly spread to neighboring
villages. In total, 15 villages reported cases; the number
of reported cases ranged from 2 to 22 cases per village.
Seventy five percent of children less than 5 years reported having been vaccinated against measles while
none had been vaccinated against rubella. All cases
were treated as outpatients and there were no deaths.
Using the passive rubella surveillance system where all
measles negative samples are tested for rubella IgM, the
number of rubella positive cases in Kenya varies by year,
month and geographical location. The number of confirmed rubella cases was 473 in 2010, 604 in 2011, 300
in 2012, 336 in 2013 and 646 in 2014. Thirty two percent of the cases were aged less than 5 years while 80 %
were aged less than 10 years. Fifty five per cent of the
cases were female with only 3 % of them being in the
reproductive age group. Overall, only 1.6 % of the cases
were women of reproductive age group.
The cases varied by month in all the years but common peaks were noted in the months of March, July and
October (Fig. 3). Cases were reported from a majority of
the 47 counties, with 40 counties (85 %) reporting cases
in 2010, 46 counties (96 %) in 2011, 40 counties (85 %)
in 2012, 39 counties (83 %) in 2013 and 45 counties
(96 %) in 2014. The highest number of cases (646) was
reported in 2014 and included 45 (96 %) counties. The
number of cases varied by county with Nakuru County
reporting one of the highest cases in 2014 (Fig. 4).
Discussion
This is the first rubella outbreak detected, investigated
and documented in the country. Previous rubella cases
Fig. 2 Age distribution of Rubella outbreak cases, Njoro District,
Kenya, 2014
Njeru et al. BMC Infectious Diseases (2015) 15:245
Fig. 3 Distribution of laboratory confirmed Rubella cases by month
and year, Kenya, 2010–2014
captured by measles case-based surveillance system
have been sporadic throughout Kenya. The index case
in this outbreak was a child who visited another district experiencing an outbreak. We attributed this outbreak to the fact that our country does not currently
provide RCV in the National Immunization Program;
therefore most of the children were susceptible to the
disease.
Studies in other countries not providing RCVs have
also demonstrated widespread transmission [23–25]. An
example of such an outbreak occurred in India when
the country was not providing RCV in their National
Immunization Program [26]. Where outbreaks have occurred in countries which immunize against rubella,
Fig. 4 Distribution of laboratory confirmed Rubella cases, Kenya, 2014
Page 4 of 6
cases have been restricted to pockets of non-immunized
individuals [27–33].
Many cases of rubella are identified every year in
Kenya by the measles surveillance system (Figs. 3 and 4).
However, there is currently no effective intervention for
rubella in the country; this is in stark contrast to measles
outbreaks which are promptly followed up with vaccination campaigns.
With regard to seasonality, this outbreak started in
March which is one of the 3 months with the highest
number of rubella cases every year. The other months
with large numbers of rubella cases are July and October
(Fig. 3). These months are characterized by a rainy season and cold weather, resulting in increased cases of
respiratory disease; this could explain the high number
of rubella cases reported during these months.
The data we obtained demonstrates that over the
years the country has consistently detected numerous
rubella cases, in spite of the low sensitivity of the passive surveillance system. The high proportion of Kenya
counties reporting rubella cases is an indicator of wider
transmission. Additionally, our data confirms the assertion of Kombich et al. that the virus is widely prevalent
among children in Kenya [20].
Six percent of the outbreak cases and 1.6 % of the routine rubella data were women of reproductive age. The
low percentage of affected women as indicated by the
routine data could be an underestimation of the true
burden as this is a passive surveillance system and many
Njeru et al. BMC Infectious Diseases (2015) 15:245
adult women are unlikely to seek health care when the
disease is mild or asymptomatic.
Kenya like many other African countries does not currently provide RCV within the national immunization
program, and a surveillance system for CRS does not
currently exist. In order to document the burden of CRS,
the country should consider establishing a CRS surveillance system. The country could also consider adopting
the WHO policy on rubella vaccination which currently
recommends combining measles and rubella control
strategies and planning efforts which focus on the widespread use of measles-rubella vaccine [34].
This outbreak report has several limitations. First, the
passive rubella surveillance system may have grossly
underestimated the magnitude of the outbreak. Many
asymptomatic rubella cases or those with mild symptoms may have been missed as they may not have sought
healthcare. Secondly, the annual number of nationally
confirmed rubella cases may also be a gross underestimation of the total burden of cases, as these data are
derived from the measles surveillance system and not a
rubella-specific surveillance system. Thirdly, many adults
including women of reproductive age could also have
been missed by the surveillance system as many may not
have sought health care owing to the mild nature of the
disease.
Conclusions
This outbreak documented that large rubella outbreaks
occur in countries without rubella vaccination programs.
Evaluation of 5 years of rubella data shows that the
disease is endemic throughout the country, therefore
outbreaks may be largely underestimated and undocumented. The fact that 6 % of all cases in this outbreak
were women of reproductive age indicates that the
threat of CRS is real. It is therefore important for Kenya
to initiate CRS surveillance to quantify the actual burden
with the goal of introducing rubella vaccine in the
future.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
IN, DO and EK participated in the outbreak investigations in the field. YA
analyzed the data that were collected in the field. All authors participated in
the drafting and approval of the manuscript.
Acknowledgements
We would like to acknowledge the support provided by the Nakuru County
Health Department during the field investigations. We would also like to
acknowledge Richard Koech (Nurse atTuiyotich Dispensary) and Jane Kinoti
(District Disease Surveillance Officer) who assisted with the investigations.
Author details
1
Disease Surveillance and Response Unit, Ministry of Health, Nairobi, Kenya.
2
Department of Health, Nakuru County, Nakuru, Kenya.
Page 5 of 6
Received: 7 September 2014 Accepted: 18 June 2015
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