Friday 29 April 2016

Zika virus (ZIKV) disease in Brazil (not just microcephaly) gets its own report...kinda

UPDATE #1: 05MAY2016
I admit I was hoping for more.

Brazil's Ministry of Health announced its first report containing dedicated Zika virus (ZIKV) numbers this week.[1] Not just the 194 detection made among diagnoses of microcephaly and central nervous system disorders,[2] but among the population as a whole. 

I was hoping for something like the Colombian data.[3]

We learned that there have been 91,387 probable cases and 3 deaths in Brazil, nationwide, up until the 2nd April 2016 and that autochthonous (local) transmission was first detected in April 2015.[1]

The report itself is a bit hard to translate though.[4] But it states that 31,616 probable cases have been confirmed. [UPDATE#1 PAHOWWHO lists 1,034 confirmed infections-a more believable figure; sad it was not clearly defined here. I infer from this that "confirmed means probable and "probable" means suspected] It does not say whether this is our old friend "clinically confirmed", or if an actual sample was collected and put through an actual test to see that there was any specific trace of ZIKV or its actual antibody produced in response to infection. This report would be greatly helped by a lot of definitions.

Geographically, Most ZIKV probable cases (39%) were in the south-east followed closely by 33% in the north-east, from where the majority of the world's temporally related M&CD diagnoses have been reported. After that there is a big step down to 19% of probable cases in the west, 7% in the north and 2% in the south. 

The highest incidence (cases per 100,000 population) occurred in the mid-west (113.4), followed by the north-east (53.5), south-east (41.4) north (36.0) and south (6.1). It would be very interesting to see this breakdown over time to observe whether ZIKV has moved during this reporting period and if so, in what direction, when and at what speed. 
From MMWR article.[5]

Overall, Brazil reports an incidence of 44.7 ZIKV cases per 100,000 people. These are only symptomatic people though, and it remains an open question as to whether the Yap Island ~80% asymptomatic rate that is so widely used and quoted,[6] holds in the Americas epidemic. As recent study of travellers who moved to or returned back to the United States after travel to ZIKV-affected countries,  found few ZIKV positives except among those with symptoms - and relevant ones at that (Fever, rash, arthralgia, or conjunctivitis).[5]
From PAHO-WHO report.

We also learned that here had been 802,429 probable cases of Dengue and 140 associated deaths as well as 39,017 cases of Chikungunya and 15 deaths - over the same period. With so many similar diseases around, I continue to boggle at how "clinically confirmed" Zika virus disease can carry much weight at all - no matter how distinctive the rash looks. Just look at the overlap in the latest PAHO-WHO report's graph above. How do you untangle prevalence let alone causality, without more lab testing?

So, with that, I look forward to Colombia's epidemiology report this weekend.

  1. Added PAHO-WHO data on actual confirmed ZIKV infections - 1,034 from new reference, [8]
  2. .

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