Saturday 7 May 2016

Brazil's microcephaly and CNS disorder (M&CD) monitoring: Report No. 24, 2016-Week No. 17...

These graphs are made by me using data obtained from epidemiological week (EW) number 17's Brazil Ministry of Health microcephaly and foetal and infant microcephaly and central nervous system (CNS) disorders (M&CD) report.[1]

Brazil reports a total of 120,161 suspected Zika virus detections this EW.[1] Around one thousand of these have been laboratory confirmed.

Suspected M&CD cases...

The total number of suspected M&CD cases increased by 115 to 7,343 this EW.

The graph above shows the number of suspected M&CD diagnoses in Brazil up to 30-April-2016. The cumulative curve (yellow dots; left hand axis) is growing, but slowly. 

This was another slower weekly rise (orange bars; right-hand axis). These bars are based on the difference in total suspected cases reported this EW compared to that reported in the last EW. This method may not reflect the diagnoses that occurred during the past EW (some may have come from days or weeks earlier), but that level of detail is not available in the MOH report.

Confirmed and discarded M&CD diagnoses...

M&CD cases under investigation decreased by 130 to 3,580 this week - the sixth consecutive decrease. This may be occurring for a range of (guessed) reasons including:

  1. improved capacity to address a large volume of request for clinical classification of suspect diagnoses.
  2. streamlining the confirmation processes
  3. retrospective application of changed head circumference definitions resulting in reductions to the number of the microcephaly diagnoses.
    This aspect will not reduce the number of cases with structural brain changes that occur in the absence of a decreased head size - which are reportedly also related to Zika virus and/or other causal influences.
    There is time involved in making these diagnoses because of the need for detailed ultrasound and other diagnostic investigations to identify congenital infection outcomes including intracranial calcifications, dilation of cerebral ventricles or posterior fossa changes and other issues.

In the graph above, we can see that 172 (blue bars; right hand axis) suspected M&CD diagnoses were discarded upon closer investigation with a current total of 2,492 removed.

The rate of these resolved diagnoses (line with blue dots, left-hand axis) continues to outpace the rate of the smaller overall number of confirmed M&CD diagnoses (red dots, left-hand axis). 

As of this EW, 17% of suspected M&CD diagnoses have been confirmed while 34% of suspected diagnoses have been discarded. 

The cumulative number of M&CD diagnoses does continue its climb this EW, growing by 73 new diagnoses (red bars; right-hand axis) to total 1,271

The number of these M&CD diagnoses to be confirmed with a Zika virus infection also grows (green dots; left-hand axis) by 9 new detections to 203 this EW (green bars; right-hand axis). Those confirmed Zika virus infections represent 16% of all confirmed M&CD diagnoses and 3% of all suspect diagnoses - but these are not fair comparisons for a range of reasons I won't go on about here.



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