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Prevalence of undiagnosed HIV infection in the general population having blood tests within primary care in Madrid, Spain
  1. Santiago Moreno1,
  2. María Ordobás2,
  3. Juan Carlos Sanz2,
  4. Belén Ramos2,
  5. Jenaro Astray2,
  6. Marta Ortiz3,
  7. Juan García2,
  8. Julia del Amo3
  1. 1Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Universidad de Alcalá de Henares, Madrid, Spain
  2. 2Epidemiologia, Consejería de Sanidad, Madrid, Spain
  3. 3Instituto de Salud Carlos III, Ministry of Health, Madrid, Spain
  1. Correspondence to Dr Julia del Amo, National Center of Epidemiology, Instituto de Salud Carlos III, C/Sinesio Delgado 6, 28029 Madrid, Spain; jdamo{at}isciii.es

Abstract

Objective To estimate the prevalence of undiagnosed HIV infection in men and women aged 16–80 years, having blood tests within primary care in Madrid, Spain.

Methods A serosurvey to monitor vaccine-preventable diseases in the general population aged 16–80 years was conducted in 2008–2009. Eligible individuals were those having blood tests. The blood extraction centres, the primary sampling units, were chosen in proportion to the size and socio-economic characteristics of the target population, aiming for a sample size of 5355 subjects with equal sex distribution within five age bands. Migrants aged 16–40 years were oversampled. Previous HIV diagnoses were excluded. Prevalence rates of HIV infection with 95% CIs were estimated allocating weights inverse to their probability of selection.

Results Overall, 3695 subjects agreed to participate, yielding a response rate of 69%, similar for men (66%) and women (73%); individuals recruited at healthcare centres or by telephone; and for all age groups except those aged ≥60 (57%) years. HIV infection was diagnosed in 12 subjects (0.35%; 95% CI 0.13 to 0.57); prevalence, higher in men (0.51%; 95% CI 0.12 to 0.89) than in women (0.20%; 95% CI 0.00 to 0.44); participants from other countries (0.61%; 95% CI 0.03 to 1.18) as compared with Spanish born (0.30%; 95% CI 0.06 to 0.53) and aged 21–30 years (0.65%; 95% CI 0.01 to 1.29), or 31–40 years (0.71%; 95% CI 0.02 to 1.41). None of the differences were statistically significant. Most of the 12 subjects were under follow-up for medical conditions; 11 had visited the primary care clinic in the preceding month.

Conclusion The prevalence of undiagnosed HIV infection is very high and calls for strategies to unveil occult HIV infection.

  • Undiagnosed HIV infection
  • early diagnosis
  • HIV testing
  • anogenital cancer
  • commercial sex
  • epidemiology (general)
  • ethnicity
  • gender
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Introduction

Half the HIV-positive subjects in industrialised countries are diagnosed late, and up to one-third of HIV-infected individuals in Europe are unaware of their status.1 ,2 Prevalence of advanced HIV diagnosis in Spain ranges from 32% to 37%.3 ,4 Expanded HIV testing is cost-effective in populations with undiagnosed HIV prevalence over 0.1%,5–7 but data on undiagnosed HIV prevalence are often unavailable. In the context of a serosurvey to monitor antibody prevalence against vaccine-preventable diseases, we estimated prevalence of undiagnosed HIV infection in men and women aged 16–80 years having blood tests within primary care in 2008–2009 in Madrid, Spain.

Methods

A serosurvey to monitor vaccine-preventable diseases in the general population aged 16–80 years was conducted in Madrid in 2008–2009. Eligible individuals were those having blood tests requested by their family doctor at public primary care blood extraction centres. People waiting to have samples of their blood taken were invited to participate in the survey by interviewers, and were requested to answer a face-to-face interview. They were informed that some of the blood—drawn for other purposes—would be tested for antibodies against infectious diseases in vaccination schedules, and would be anonymously tested for other infections of public health relevance. Information on age, sex, country of origin, educational level (primary, lower and upper secondary and university) and social class (based on occupation into groups I–V) was collected. Participants were asked about reasons for blood extraction and the number of recent visits to the clinic. No information was collected on intravenous drug use or sexual habits. Patients were specifically asked whether they had ever been diagnosed with ‘immunosuppressive disorders without explicitly mentioning HIV’ or hepatitis. Persons who self-identified having a blood extraction for HIV-related reasons were excluded.

Blood extraction centres, the primary sampling units, were chosen in proportion to size and socio-economic characteristics of the ascribed population, aiming for a sample size of 5355 subjects with equal sex distribution within five age bands. Migrants aged 16–40 years were oversampled. The population denominator was 6 271 638 inhabitants. As the targeted number of participants with pre-defined age, sex and characteristics of origin could not be reached during the recruiting period, additional recruitment of 309 subjects (8.4%) was conducted by telephone among randomly selected health-card holders.

Laboratory methods

Sera were analysed for antibodies against HIV-1 (including subtype O) and p24 antigen using enzyme-linked immunoassay (Enzygnost Anti-HIV Integral II, Siemens), and positive specimens were confirmed in quadruplicate. Specimens that repeatedly showed positive by enzyme-linked immunoassay were confirmed by Western blot analysis (rgp 120, rgp 41, rHIV-2, rp 31, rp 24/26) (Chiron Riba HIV-1/HIV-2) at the National Public Health Reference Laboratory.

Statistical analysis

Prevalence of HIV infection with 95% CIs was estimated by allocating weights inverse to their probability of selection. Analyses were performed with SPSS V.9.0 and STATA 6.0.

The study was approved by the Ethics Committee of Hospital Ramón y Cajal, Madrid. Participants signed an informed consent.

Results

Overall, 3695 of the 5355 subjects agreed to participate, yielding a response rate of 69%, similar for men (66%) and women (73%), individuals recruited at healthcare centres or by telephone, and for all age groups except those aged ≥60 (57%) years. The main reasons for not participating were ‘lack of interest’ (57%) and ‘lack of time’ (21%). Eight subjects who reported having blood extractions for HIV-related reasons were excluded.

Of the 3695 participants, 53% were women, mean age was 37.9 years, 25% were born outside Spain; Ecuador (19%), Rumania (11%) and Colombia (10.5%). Other socio-demographic characteristics are summarised in table 1.

Table 1

Prevalence of HIV infection according to sample characteristics

HIV infection was newly detected in 12 persons; weighted HIV prevalence 0.35% (95% CI 0.13 to 0.57). HIV prevalence by sex, age, origin, educational level and social class are summarised in table 1. HIV prevalence, overall, and by socio-demographic characteristics, did not vary when the 309 subjects recruited by phone were excluded.

Most of the 12 subjects who tested HIV positive were under follow-up for medical conditions; abnormal liver function tests (n=5), anaemia (n=2), hyperthyroidism (n=1) and hypercholesterolaemia (n=1). Eleven individuals testing positive had visited the primary care clinic in the preceding month.

Discussion

We report a high prevalence of undiagnosed HIV infection in a representative sample of the population aged 16–80 years who visited primary care centres in Madrid. Prevalence was higher in men, people aged 20–40 years and in those born outside Spain, but the differences were not statistically significant.

Misclassification of people who were previously diagnosed with HIV may have led to an overestimation of HIV prevalence but we think that, although possible, it is unlikely that this has played a major role as participants were asked about the reasons for blood extraction; eight persons reporting an HIV-related reason were excluded. Subjects were also asked if they had been previously diagnosed with disorders leading to immune suppression as an indirect way of recalling HIV infection and, had subjects been unwilling to disclose their HIV status, they could have refused to participate in the survey rather than providing incorrect information. In addition, HIV-positive subjects in Spain are seen almost exclusively at hospital HIV-care units, even for minor complaints.

The prevalence of HIV was found to be both global and for ages 16–40 years, similar to that found in an unlinked anonymous survey for vaccine-preventable diseases in the Spanish population (excluding Catalonia) in 1996 (0.43%, 95% CI 0.15% to 1.07%).8 Its high prevalence in migrants is consistent with the epidemiology of HIV infection in Spain.3

Most people identified as HIV positive had visited primary healthcare centres at least once in the preceding month, highlighting missed opportunities to diagnose HIV in primary healthcare. Yazdanpanah et al published a cost-effective model for expanding HIV testing to the general population in primary care in France, and have reported this to be cost-effective for prevalence of 0.1% of undiagnosed HIV, and a test acceptance of 79%.9 Both, point estimates and the lower limit of 95% CI in our study were higher than those considered cost-effective for offering voluntary HIV testing to the general population in France, but the acceptance rate for testing was lower. In conclusion, previously undiagnosed HIV infection in Madrid is very high and calls for strategies to unveil occult HIV infection.10

Key messages

  • Prevalence of previously undiagnosed HIV infection in the population aged 16–80 years who have had a blood test taken in primary care in Madrid is very high; 0.35% (95% CI 0.13 to 0.57).

  • Most of the subjects newly detected with HIV infection who were previously unaware of their HIV status had very recently used the public health system highlighting missed opportunities for HIV diagnosis.

References

View Abstract

Footnotes

  • Healthcare in Spain is universal and also covers migrants of uncertain residency status provided they are registered at the local council. Registration at the council, and not legal residency, is the prerequisite to own a health card under current Spanish law.

  • Funding This serosurvey was supported by funds from the Consejería de Sanidad Madrid, Spain, and partially supported by Gilead Sciences.

  • Competing interests Santiago Moreno has been involved in speaking activities and has received grants for research from Gilead Sciences.

  • Patient consent Obtained.

  • Ethics approval Ethics approval was provided by Ethics Board Hospital Ramon y Cajal.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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