Some Bengaluru zones still have high positivity rate

Bengaluru may have officially reached the 5 per cent test positivity rate (TPR), upon which the government can act to institute a graded unlock, but a closer look at the data shows that some zones are still striving to contain the epidemic.

Four zones, Bommanhalli, Mahadevapura, R R Nagar and East, show test positivity rates of 6 per cent or higher, according to data released on Monday from the Bruhat Bengaluru Mahanagara Palike (BBMP) war room. One expert said that these high rates could indicate that these zones are more effective in their surveillance methods, compared to those with low positivity rates.

War room data covering 10 days from May 29 to June 7 show that the caseload in these zones is the highest in the city. All but one was testing high. In the East Zone, which spans 44 wards and an area of over 142 square kilometres, only an average of 173 tests were being done per ward per day.

In contrast, the large Bommanahalli zone (spanning 125 square km) did 747 tests per ward per day. The data shows that Bommanhalli, which has a TPR of 6.2 per cent, was finding some of the largest numbers of infected people daily (738 compared to 454 in East).

Bommanhalli’s Special Officer, Rajender Kataria said the large and scattered nature of the zone had challenged containment. “Cases are mostly being found in hotspots, like villages and slums. Our TPR has dropped from 34-35 per cent two weeks ago,” he said.

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Pointing to the fluctuating nature of the rate, the zone’s Monday-specific positivity rate was 2.7 per cent.

At Mahadevapura zone, apartment dwellers are still driving the outbreak, followed by slum residents. A zonal official specified that an average of 541 tests are being conducted per ward per day. “High mobility, especially by construction workers, is creating another dynamic of infection,” the officer said.

For unlocking to be considered, the aggregated, city-wide TPR will be considered, explained the municipal Chief Commissioner, Gaurav Gupta. “Some zones are bound to have a higher rate than others,” he added.

Low numbers, low efficiency?

But why is the positivity rate so different across a largely homogeneous city? Epidemiologist Dr Giridhar Babu pointed out that conditions for spread across the city are technically the same. “Spread may vary due to population density but the only difference is surveillance and testing,” he said.

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He pointed out that zones where the positivity rate is low such South, West and Dasrahalli, could actually be suggestive of problems.

According to data, these zones, which sport a positivity rate of under 4 per cent, have one thing in common: low testing rates per ward. South Zone conducted 185 tests per day per ward over the last 10 days and found 242 cases per day.

However, Dr Shivakumar, Zonal Health Officer, said that the low testing cannot be used as a metric. “Just two weeks ago, if we tested 100 people, 40 people were found positive. Today, it is only two or three. The worst is over,” he said.