Social mixing patterns relevant to infectious diseases spread by close contact in urban Blantyre, Malawi

Abstract

IntroductionUnderstanding human mixing patterns relevant to infectious diseases spread through close contact is vital for modelling transmission dynamics and optimisation of disease control strategies. Mixing patterns in low-income countries like Malawi are not well understood.MethodologyWe conducted a social mixing survey in urban Blantyre, Malawi between April and July 2021 (between the 2nd and 3rd wave of COVID-19 infections). Participants living in densely-populated neighbourhoods were randomly sampled and, if they consented, reported their physical and non-physical contacts within and outside homes lasting at least 5 minutes during the previous day. Age-specific mixing rates were calculated, and a negative binomial mixed effects model was used to estimate determinants of contact behaviour.ResultsOf 1,201 individuals enrolled, 702 (58.5%) were female, the median age was 15 years (interquartile range [IQR] 5-32) and 127 (10.6%) were HIV-positive. On average, participants reported 10.3 contacts per day (range: 1-25). Mixing patterns were highly age-assortative, particularly those within the community and with skin-to-skin contact. Adults aged 20-49y reported the most contacts (median:11, IQR: 8-15) of all age groups; 38% (95%CI: 16-63) more than infants (median: 8, IQR: 5-10), who had the least contacts. Household contact frequency increased by 3% (95%CI 2-5) per additional household member. Unemployed participants had 15% (95%CI: 9-21) fewer contacts than other adults. Among long range (>30 meters away from home) contacts, secondary school children had the largest median contact distance from home (257m, IQR 78-761). HIV-positive status in adults >18 years-old was not associated with increased contact patterns (1%, 95%CI -9-12). During this period of relatively low COVID-19 incidence in Malawi, 301 (25.1%) individuals stated that they had limited their contact with others due to COVID-19 precautions; however, their reported contacts were not fewer (8%, 95%CI 1-13).ConclusionIn urban Malawi, contact rates, are high and age-assortative, with little behavioural change due to either HIV-status or COVID-19 circulation. This highlights the limits of contact-restriction-based mitigation strategies in such settings and the need for pandemic preparedness to better understand how contact reductions can be enabled and motivated.

Risk factors for pneumococcal carriage in adults living with HIV on antiretroviral therapy in the infant pneumococcal vaccine era in Malawi

“…VT carriage acquisition between mothers and their infants has been demonstrated previously in Malawi and South Africa prior to infant-PCV introduction 20,21 . Thus, our finding aligns with recent evidence in the same setting showing strong intergenerational social mixing patterns between females and their potentially PCV13-vaccinated younger children likely through parental or guardian roles 46 . This suggests that in the infant-PCV13 era, interruption of VT carriage transmission likely favors females than males.…”

“…Higher overall and VT carriage prevalences among younger than older adults reported in this study may suggest distinct high carriage acquisition risk in younger adults, partly supported by recent evidence of higher rates of skin-to-skin contacts between younger adults and with other age groups in urban Blantyre 46 . The shorter median duration on ART amongst the younger adults as shown in S6 Fig may contribute to this residual pneumococcal carriage through incomplete immune reconstitution at both the systemic and mucosal level 27,47,48 .…”

“…Low SES neighbourhoods in urban Blantyre predominantly comprise high-density informal settlements, relatively larger households and low rates of formal employment 28 . Thus, substantial overall carriage prevalence in younger adults from low SES suggests that factors associated with low SES such as poorly ventilated and overcrowded houses with intense social contacts are reservoirs for pneumococcal carriage in the PCV13 era 16,28,46,49 . On the contrary, non-differential VT carriage prevalence by household SES underlines an important role PCV vaccination plays to outweigh infection risks in poor settings.…”

Characterizing social contact patterns in rural and urban Mozambique: the GlobalMix study, 2021-2022

“…Compared to pandemic periods in Kenya [7] and Malawi [6], we observed lower mean number of contacts in Mozambique but a higher number of contacts reported by participants in the rural compared to the urban site. However, we interpret this with care since data from Kenya and Malawi were collected from high-density settlements where individuals may have been unable to fully adhere to physical distancing mainly due to economic reasons.…”

“…Lastly, we computed age-stratified contact matrices to quantify the interactions between age groups. We adjusted the contact matrices to account for reciprocity, assuming that the total number of contacts from age group ݅ to ݆ were equal to the number of contacts from age group ݆ to ݅ i.e., ݉ , = ݉ , [6]. We present the age-specific contact matrix using data from day 1 only using the revised formula ሺሺ݉ , ݉ , ሻ/ሺ݊ ݊ ሻሻ which does not adjust for Mozambique agespecific population size.…”