in HIV spread in four sub-Saharan African cities
the multi-site study*
In many large
towns in Central, East and southern Africa the HIV prevalence
rate among pregnant women currently exceeds 30%, while in the
cities and towns of most of West Africa fewer than 10% of pregnant
women are infected. What accounts for these enormous variations?
Some urban populations admittedly have a longer-standing epidemic
than others, but the time factor alone does not explain all the
differences. Clearly, HIV has been spreading at different rates
in different populations.
more about this differential rate of spread, a multi-site study
was carried out in four African towns with differing HIV prevalence
trends in pregnant women. Kisumu (Kenya) and Ndola (Zambia), in
Central/East Africa, were selected as the towns with high HIV
prevalence, while the low-prevalence towns in West Africa were
Cotonou (Benin) and Yaoundé (Cameroon).
1997 and March 1998, surveys were carried out in all four sites
behaviour patterns - e.g. age of sexual initiation and marriage,
number of sex partners, contacts with prostitutes - which may
determine the probability of exposure to an infected partner
- e.g. condom use, other sexually transmitted diseases, male
circumcision - which may determine the probability of HIV transmission
for the study was obtained from the national ethics committee
in each of the countries where the study took place, as well as
from other ethics committees. The general population survey in
each town aimed at a random sample size of 1000 men and 1000 women
aged 15 to 49 years. Households were visited by a team of interviewers
and nurses or doctors. The survey of sex workers was preceded
by mapping all places where prostitutes could be found and recording
the number of sex workers present in each location at the time
of the study team's visit, so that a representative sample of
about 300 prostitutes could be selected in each town.
their informed oral consent, study participants were interviewed
on their socio-demographic characteristics and sexual behaviour,
using a standardized questionnaire, and were asked to give a blood
sample and urine sample. HIV testing was done anonymously, but
the result was linked to the interview data and to the results
of the laboratory tests for HIV and for the presence of sexually
transmitted diseases (STDs) including syphilis, gonorrhoea, genital
herpes (HSV-2) and trichomonas infection. Study participants who
wished to know their HIV serostatus were referred for pre- and
post-test counselling and re-testing, free of charge. Study participants
with symptoms and/or signs suggestive of an STD were treated.
* The full
report of the multi-site study has been submitted for publication.
of HIV infection
of HIV infection in men (aged 15-49) was 3% in Cotonou, 4% in
Yaoundé, 20% in Kisumu and 23% in Ndola. For women, the respective
prevalence rates were 3%, 8%, 30% and 32%.
In all sites,
except Cotonou, overall prevalence was significantly higher in
women than in men. The largest male/female divergence was found
among 15-19-year-olds in Kisumu and Ndola. In Kisumu, over 3%
of male teenagers were infected, compared with 23% of female teenagers.
In Ndola, HIV prevalence in this age group was 4% in boys and
15% in girls.
of HIV infection among sex workers was extremely high in the two
high-prevalence sites (Kisumu, almost 75%; Ndola, 68%) compared
with Yaoundé (33%), although the prevalence in Cotonou (over 57%)
was also quite high. Across these four sites 40% of the prostitutes
were 24 years old or younger, with a figure of 56% in Ndola. Almost
a quarter of prostitutes in Ndola were under 20.
In the two
low-prevalence sites and in Kisumu, more than 70% of circulating
HIV-1 strains belonged to subtype A. In Ndola practically all
circulating strains were subtype C. The biggest range of strains
was see in Yaoundé, where subtypes A, D, E, F, G and H were found,
as well as strains belonging to group O.
debut and marriage
In all sites,
between 97% and 99% of men and of women 20 years old and above
reported having had sexual intercourse. However, among 15-19-year-olds
the proportion of those who were sexually active ranged from under
50% in Cotonou to just over 70% in Kisumu. For both males and
females, age at first sexual intercourse was lowest in Kisumu
and highest in Cotonou. Significantly more girls in Kisumu and
Ndola had their sexual debut before age 15 than in the two low-prevalence
of men and women who were currently-married or ever-married was
significantly higher in Kisumu and Ndola than in the low-prevalence
sites. Similarly, age at first marriage was significantly lower
for both men and women in Kisumu and Ndola than in Cotonou and
rate of partner change was found in Yaoundé, where men reported
an average of 10 lifetime partners (compared with 5 in Kisumu
and 4 in Cotonou and Ndola) and women reported 3 (compared with
2 in the other three sites). Never-married men and women in Yaoundé
reported the largest numbers of non-spousal partners in the year
preceding the interview, followed by men and women in Kisumu.
Currently-married men in the high-prevalence sites reported fewer
non-spousal (extramarital) partners than married men in Cotonou
and Yaoundé. Extramarital relationships were reported by very
few currently-married women (1-3%) except in Yaoundé, where 12%
of women reported at least one such relationship in the year before
between non-spousal partners
between non-spousal partners were similar in Cotonou, Yaoundé
and Ndola, but significantly smaller in the high-prevalence site,
Kisumu. The age difference between non-spousal partners, as reported
by men, was 4 in Cotonou and Yaoundé, 3 in Kisumu and 4 in Ndola,
the male partner always being older. However, among married -
teenage girls living in Kisumu and Ndola, the older their husband
(and the larger the age difference between the partners), the
higher their risk of being HIV-infected.
with sex workers
of men reporting at least one contact with a sex worker in the
past year was almost 7% for Cotonou, 13% for Yaoundé, almost 7%
for Kisumu and 11% for Ndola. When analysis was restricted to
men who reported having non-spousal partnerships in the year before
interview, the percentage having contact with a prostitute was
significantly higher in Ndola (over 32%) than in Cotonou and in
Kisumu (around 15%) and Yaoundé (almost 20%).
prevalence among sex workers tended to be higher in the high-prevalence
sites, as mentioned earlier, the HIV rate in Cotonou sex workers
was also quite high. However, use of a condom with the most recent
client was reported more often by sex workers in Cotonou than
in any other site. Of the HIV-infected sex workers in Cotonou
64% reported condom use with their last client, compared with
349% in Yaoundé, 50% in Kisumu and 30% in Ndola. When the data
on HIV prevalence and condom use with clients are examined together,
it is clear that sex work clients in Ndola and Kisumu are more
exposed to HIV infection than clients in the low-prevalence towns.
low proportion of men in all sites - ranging from 21% in Cotonou
to 25% in Ndola - reported that they often or always used condoms
with non-spousal partners. Women in the low-prevalence towns reported
less condom use than women in the high-prevalence sites.
in HIV transmission
an STD that causes genital ulcers, was by far most prevalent in
Ndola, followed by Yaoundé. Serologic evidence of current or previous
genital herpes (HSV-2 infection) - another ulcer-producing STD
-- was more common in the high-prevalence sites than in the other
two sites. Taken together, the prevalence of the two ulcerative
STDs was higher in the towns with high HIV prevalence. The differences
between the sites were especially marked among young people under
25. In all four sites HSV-2 infection was strongly associated
with an increased risk of HIV infection in both men and women.
of gonorrhoea was generally low and variable. Chlamydial infection
was more common in younger age groups, especially in girls, and
the highest prevalence was in Yaoundé, followed by Kisumu. The
highest rates of trichomonas infection were found in women in
Kisumu and Ndola (29% and 34%).
and Yaoundé nearly all men reported being circumcised, while in
Ndola only 10% of men were circumcised. In Kisumu, where the overall
percentage of circumcised men was less than 30%, HIV prevalence
was below 8% in men circumcised before their sexual debut and
25% in uncircumcised men. In multivariate analysis, being circumcised
was associated with a lower risk of HIV infection .
In our study
the only differences in sexual behaviour that distinguished Kisumu
and Ndola from Cotonou and Yaoundé concerned the age at which
girls became sexually active, and the age at which men and women
first married. Compared with the low-prevalence sites, in Kisumu
and Ndola females were younger at sexual debut and both sexes
married earlier. In Kisumu, moreover, teenage girls whose husbands
were older were more likely to be HIV-infected. High rates of
partner change, contacts with sex workers, and concurrent sexual
partnerships, were not reported more systematically in the high-prevalence
than in the low-prevalence sites.
data, it would be difficult to argue that the divergence in the
rate of HIV spread between the East African and West African sites
can be explained solely by differences in sexual behaviour.
Nor was there
evidence that differences in circulating strains of HIV-1 are
a major factor in the rate of spread of HIV. Subtype A was the
most prevalent subtype in both of the low-prevalence sites as
well as in one high-prevalence site.
study did find associations between higher HIV rates and two biological
co-factors, suggesting that these might have contributed to a
higher probability of HIV transmission during sexual intercourse
in the high-prevalence sites.
had already established that HIV transmission is enhanced in the
presence of another STD, particularly an STD causing genital ulcers.
The multi-site study found that significantly more people in Kisumu
and Ndola, especially in the 15-24 age bracket, had serologic
evidence of current or previous infection with an ulcerative STD
(syphilis and genital herpes).
the study found large differences between the sites in the percentage
of men circumcised. In Cotonou and Yaoundé, cities where over
97% of men are circumcised, lower HIV rates were found than in
Kisumu and Ndola, where the percentage of men circumcised ranges
from 10% to less than 30%. In the high HIV prevalence sites, moreover,
close to 16% of young men under 25 had an ulcerative STD, whereas
in the low-prevalence sites the figure was 6%-8%. Lack of circumcision
was thus associated with higher rates of both HIV and ulcerative
STDs, the latter in turn possibly raising the HIV transmission
can one explain the dramatically high prevalence of HIV infection
(15%-23%) in girls under 20 in Kisumu and Ndola? Unmarried girls
in these cities reported a median of 1 to 1.5 lifetime sex partners,
an estimated 10-12% of whom were HIV infected. A separate qualititative
study carried out in Kisumu has found evidence of early sex with
older partners (men aged 25 and above) among teenage girls, both
married and unmarried. This suggests that the teenagers in the
multi-site study may have under-reported their number of partners,
especially non-spousal partners older than 25. Partners like these
are likely to have exposed the girls to the virus, since HIV prevalence
in Kisumu and Ndola among men aged 25 and over ranged from 26%
these factors are taken into account, however, it is hard to explain
the high HIV prevalence in female teenagers. For the girls to
have become infected so soon after their sexual debut as a result
of relatively few exposures to an infected partner, HIV transmission
co-factors must be part of the explanation. In this connection
it is important to recall that almost 50% of the 15-19-year-old
girls in Kisumu and Ndola had been exposed to the virus that causes
genital herpes and almost 16% had syphilis.
differences in the rate of HIV spread between the East African
and West African cities studied cannot be explained away by differences
in sexual behaviour alone. In fact, behavioural differences seem
to be outweighed by differences in HIV transmission probability.
of our findings for the prevention measures are complex. For instance,
if further studies prove that male circumcision is really protective,
it would be important to assess carefully the benefits as well
as the practical risks of the procedure under field conditions,
including the risks of infection and haemorrhage. With respect
to the ulcerative STDs, while syphilis is curable there are no
drugs that can cure or reduce the transmission of genital herpes
-- a lifelong viral infection. Herpes can, however, be prevented
through condom use, and research is in progress to develop a vaccine.
On the other
findings should not be interpreted as a denial of the important
role that sexual behaviour change and improved STD care can play
in curbing the HIV epidemic. First of all, even the "low" HIV
prevalence sites studied have considerable rates of HIV infection,
and even in the high-prevalence sites barely a quarter of men
reported that they often or always used condoms with non-spousal
partners. The risk behaviours identified in all four sites call
for scaled-up and sustained action in the areas of condom promotion,
education for safer sexual behaviour, and diagnosis and treatment
of the curable STDs.
given the high levels of HIV infection in young women in Kisumu
and Ndola, effective interventions are urgently needed to decrease
their vulnerability. Girls must be made aware that they run an
enormous risk of becoming infected with ulcerative STDs, HIV,
or both, during their first few exposures to sex, especially with
an older man, who is far more likely to be infected than boys
their own age. Girls should learn the necessary life-skills to
stand up to demands for early, unwanted or unsafe intercourse.
since men still play the dominant role in deciding whether and
under what circumstances sex will take place, priority must be
given to sexual behaviour change programmes aimed at them. Social
pressure should be put on older men to avoid forcing or coercing
young girls into sex, or enticing them with sugar-daddy gifts.
Cross-generational sex exposes girls to lethal risk and helps
drive the HIV epidemic.
the Study Group on Heterogeneity of HIV Epidemics in African Cities
are: A Buvé (coordinator), M Laga, E Van Dyck, W Janssens, L Heyndricks
(Institute of Tropical Medicine, Belgium); S Anagonou (Programme
national de Lutte contre le SIDA, Benin); M Laourou (Institut
national de Statistiques et d'Analyses économiques, Benin); L
Kanhonou (Centre de Recherche en Reproduction humaine et en Démographie,
Benin); Evina Akam, M de Loenzien (Institut de Formation et de
Recherche démographiques, Cameroon); S-C Abega (Université Catholique
d'Afrique Centrale, Cameroon); Zekeng (Programme de Lutte contre
le SIDA, Cameroon); J Chege (The Population Council, Kenya); V
Kimani, J Olenja (University of Nairobi, Kenya); M Kahindo (National
AIDS/STD Control Programme, Kenya); F Kaona, R Musonda, T Sukwa
(Tropical Diseases Research Centre, Zambia); N Rutenberg (The
Population Council, USA); B Auvert, E Lagarde (INSERM U88, France);
B Ferry, N Lydié (Centre français sur la population et le développement,
France); R Hayes, L Morison, H Weiss, J Glynn (London School of
Hygiene & Tropical Medicine, UK); NJ Robinson (Glaxo Wellcome,
UK); (M Caraël (UNAIDS, Switzerland).
more information, please contact Anne
Winter, UNAIDS, (+41 22 791.4577)