In this provincially representative sample of 3,557 women, the adapted WRAT-3 was reliable and valid for measuring general literacy and numeracy. Poor literacy and numeracy were common for women living in Zambézia Province, and similarly many women had difficulty with items that assessed basic numerical concepts and computational skills. For both Portuguese speakers and non-speakers, poorer literacy and numeracy skills were associated with less HIV knowledge but not lower self-reported utilization of HIV testing or prenatal care. To our knowledge, this is the first study in the literature that reports directly measured literacy and numeracy skill in a representative population in rural sub-Saharan Africa. Our use of representative data to estimate the literacy and numeracy skills for all female heads-of-household in the province is a major strength of this study.
The prevalence of illiteracy in our study is substantial, and higher than the recent estimate of the Mozambican national literacy rate of 54%. 
We assessed literacy in a group of women living in predominantly rural settings who had a low level of formal education, likely explaining these differences. This study builds on other work done in sub-Saharan Africa to estimate literacy by utilizing a direct test of individual literacy and numeracy skill, rather than estimating literacy indirectly by self-report, 
national census data, 
or directly by use of non-standardized measures of reading comprehension. 
One study adapted a validated English language test of health literacy, the Rapid Estimation of Adult Literacy in Medicine (REALM) to measure health literacy in 125 bilingual South Africans, but concluded that its use was unsuitable because poor comprehension of many of the included health terms. 
Based on our data from Zambézia, the development of language and context appropriate health literacy or functional literacy measurement tools should be a topic for further work in low and middle income settings.
The deficits in numeracy for many women in this study are stark, and may have serious implications for behaviors necessary for utilization of health care for themselves and their children. To our knowledge, previous to this study there was no measure published in the literature estimating numeracy by direct measurement in persons living in sub-Saharan Africa. Work in the US looking at literacy and medication administration have shown that individuals with low literacy have difficulty appropriately dosing liquid medications for their children 
and with managing their own medications. 
These challenges, if generalizable to HIV-affected women in Zambézia for example, may be even more important given the potential harm from too much or too little antiretroviral medication given during prevention of mother-to-child transmission care, self-care, and assistance to family members, notably treatment to children.
The positive associations of literacy and numeracy with HIV knowledge are similar to evidence from US studies among individuals living with HIV infection. 
While the literacy skills measured in this study may or may not be directly required for interaction with the health system, there is evidence that individuals with low literacy have difficulty communicating with health-care providers. 
This may be a particular problem in health care settings such as those in Zambézia, where often the language of the provider (often Portuguese) differs from the local languages in which patients have fluency and use as their primary language at home. 
The lack of association between literacy and health seeking behavior may reflect that among the multitude of barriers facing women in accessing care in rural Zambézia, literacy skills are less important to access care per se
. The use of self-reported outcomes may also limit the ability to examine these associations, as individuals with poor literacy may be more likely to be unaware of past HIV testing.
In addition to the limitation of our use of a general literacy scale in this study (vs. a functional scale), there are potential methodological limitations with using a word list for measuring literacy in the Portuguese language. The WRAT-3 reading list uses pronunciation of words as a proxy measurement for reading comprehension; while rapid to administer and valid, this approach may overestimate literacy. 
This effect has been shown to be more pronounced when using these types of literacy measures in languages such as Spanish, where there is a direct relationship between the appearance and pronunciation of a given word. 
One study that attempted to adapt a word-reading literacy test into Spanish was successful only in generating dichotomous groups of high or low literacy. 
Other limitations to this study include the cross-sectional design of the study and the use of self-reported data, making some of our findings potentially subject to confounding and recall bias. The use of a non-validated HIV knowledge scale and the fact that ten-percent of participants did not respond to the HIV-knowledge items introduces the possibility for misclassification bias. The study included data from women living in one province in rural Mozambique only, and so results may not be applicable to the male population, persons living in other Provinces, or to individuals living in more urban settings.
Our study introduces valid instruments to measure general numeracy and literacy that could be adapted for other settings and languages, and also demonstrates clearly some of the skill disparities facing women within one rural province in Mozambique. These data suggest that literacy and numeracy may be important independent factors in the acquisition of HIV knowledge, and have implications for public health efforts in rural settings such as Zambézia where literacy and numeracy skills are limited. The level of literacy and numeracy skill should be taken into consideration when developing HIV educational messages in resource-limited settings such as Zambézia. While efforts to improve primary school education access and quality for women is clearly a high national priority, interventions designed to improve the quality of provider health communication or improve the applied literacy and numeracy skills of patients during HIV care and treatment programs may be simple, inexpensive and have a more immediate impact. 
A better understanding of how literacy and numeracy skills are related to health behaviors, skills and knowledge would inform efforts to overcome health disparities and may generate new strategies to improve health care quality in settings where low literacy is common.