We found that certain clinical signs and symptoms are highly specific for HIV infection in relatively healthy infants exposed to ARVs for prevention of vertical transmission below 10 weeks of age. Any one of a complex of findings including oral thrush, lymphadenopathy, hepatomegaly, splenomegaly, weight centile, diaper dermatitis, or reflux, give specificities and sensitivities of up to 89% and 80% respectively. A small number of studies prospectively investigated clinical symptoms in acutely infected infants during breastfeeding. In a study by Rouet et al in Cote d'Ivoire, 22 of 342 infants developed postnatal HIV infection. Acute retroviral syndrome, generalised lymphadenopathy and dermatitis were predictive of acute HIV infection . Richardson et al performed a similar study in Kenya where 40 (71%) of acutely infected infants were below 2 months of age in a cohort of 189 infants. Acute infection was associated with lymphadenopathy in ≥ 2 sites and upper respiratory tract infection .
In a larger study from the pre-VTP era of infants born to HIV-infected women, the Zimbabwe Vitamin A for Mothers and Babies (ZVITAMBO) group evaluated WHO, South African, and Zimbabwean algorithms for HIV diagnosis in 6-week-old infants . In this study, 52% of HIV-infected infants had a weight for age < 50th centile (Z score ≤ 0), and by focussing on this group, the author's developed diagnostic algorithms based on clinical signs with relatively high yield. However, by focussing only on HIV-exposed infants with weight-for-age below the median, sensitivity of their clinical algorithm for HIV diagnosis was 65%. When combined with ≥ two other physical signs (e.g. pneumonia, ear discharge, treatment for TB, oral candidiasis), the sensitivity decreased to 20% but the specificity increased to 94%. Our algorithm including weight < 50th centile (algorithm B; table 3) but with different findings improved sensitivity to 86% in this age group. Additionally, a simplified algorithm that included weight < 50th maintained high sensitivity of 85%. However, algorithms of this sort exclude the high proportion of HIV-infected infants with weight above 50th centile.
The ZVITAMBO approach  of focusing where yield for subsequent DNA PCR testing may be highest appears useful in settings with severe resource limitations . South Africa is a mid-income country that can afford HIV-1 diagnostic PCRs on all HIV-exposed infants. Therefore, although limiting tests to infants below the 50th centile may reduce costs, the number of infants missed will be unacceptably high. Consequently, an algorithm with higher sensitivity would be useful. Additionally, in settings where PCR is unavailable or turnaround time for results unacceptable, an algorithm with high sensitivity may be preferred as a strategy for ART initiation to prevent the early infant mortality associated with HIV infection. Therefore using algorithm B, may be preferable in these settings. The advantage of algorithms such as ours is that programs could adapt the cut-off to suit their needs.
To our knowledge, ours is the first study to investigate diagnostic algorithms of predominantly formula fed infants in the VTP era. Our algorithms have the highest sensitivity for HIV identification of all those previously published, particularly in this age group.
The majority of other algorithms and guidelines to identify HIV-infected children have not included infants below two months of age [10–12]. Jones et al found a sensitivity of 17% when applying the Integrated Management of Childhood Illness (IMCI) algorithms for predicting pediatric HIV infection to a cohort of 301 HIV-exposed infants in VTP programs, of whom 26 (8.7%) were shown to be HIV-infected by HIV DNA PCR . However, using clinical signs similar to those selected in our study (hepatosplenomegaly, recurrent infections, failure to thrive, and candidiasis) and where doctors evaluating the infants were unaware of infection status, the sensitivity for HIV infection increased to 56% at 6 weeks of age .
As expected, increasing the number of positive signs reduces sensitivity but increases specificity. Reflux occurred at low frequency (3.4%) but appeared very specific, albeit difficult to define. Of note, 11 (73%) of the 15 infants with reflux also had oral thrush, which could have aggravated or caused the symptom; swallowing incoordination, an early sign of encephalopathy, could also have contributed. That oral thrush and low weight for age were so highly specific in this population suggests that these findings cannot only be attributed to formula feeding or co-morbidities such as malnutrition and TB.
A limitation of our study is that clinician's knowledge of the infants' HIV status may have influenced the finding and reporting of clinical findings. On the other hand, HIV-infected infants eligible for CHER were selected for lack of severe clinical disease  and doctors trained for the study evaluated all infants. Our results require validation in other settings, for example, where malaria and breastfeeding are prevalent, and in VTP programs with larger numbers of HIV-exposed uninfected infants and with lower HIV prevalence. Our study included a large group of HIV-infected infants (77%) and a smaller number of HIV-exposed infants, all below 10 weeks of age, in contrast to all of the other
studies. Also, as mentioned, infants with severe clinical disease, where the diagnosis may be more obvious, were also excluded. In settings where this algorithm would be useful, the prevalence of HIV-infection amongst exposed infants would be lower, and thus affect the positive and negative predictive values of the algorithm. In addition, due to selection methods, most HIV-infected infants included in this analysis were relatively well, with a median CD4 count of 34%. The algorithm may perform better in a general population of HIV-infected infants. Additionally, only 12% of this cohort was breastfeeding. In conclusion, a combination of clinical findings in infants below 10 weeks of age may be useful for predicting HIV infection and prioritising care. There is urgent need to validate these findings in other settings and to determine their relevance in diverse settings.