Denominators Matter

By Dr Milton Lum | 19 February 2021

The number of positive Covid-19 cases per 100,000 population in Malaysia increased from 145.04 on 15 Nov 2020 to 815.02 on 15 Feb 2021, an increase of nearly 562%.

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The cumulative numbers of positive Covid-19 cases in Malaysia have increased markedly in the past three months.

Malaysia was ranked 85 in the total cumulative positive cases in the world on 18 November 2020 – the United States was ranked 1 with the world’s highest number of positive cases.

Three months later, on 18 February 2021, Malaysia’s ranking was 45, a jump of 40 places.

The daily media statements of the Ministry of Health (MOH) contain the percentages of recoveries, cases involving Malaysians and foreigners, and deaths. However, the numbers of cumulative cases, active cases, those in intensive care units and on respirators are presented in absolute numbers. 

In short, both numerators and denominators are stated in some MOH data but denominators are not stated in other data.

When both numerators and denominators are stated, there is perspective. This is illustrated below.

Positives In Relation To Population

When the numbers of positives are stated in relation to 100,000 of the population of the states or territories, there is perspective.

The positive cases per 100,000 population in the three months from 15/11/2020 to 15/2/2021 are shown in Table 1. 

The overall positives per 100,000 population for Malaysia on 15/11/2020 was 145.04. The top three were Labuan (1,181.73), Sabah (590.73), and Negeri Sembilan (302.88), whilst the bottom three were Kelantan (11.03), Perlis (16.07), and Terengganu (17.82). 

The overall positives per 100,000 population for Malaysia on 15/2/2021 was 815.02, an increase of 561.88% from 15/11/2020. The top three were Labuan (2,233.94), Kuala Lumpur (1,806.60), and Selangor (1,342.03), whilst the bottom three were Perlis (76.05), Pahang (210.72), and Terengganu (231.53).

The top three increases during the three-month period from 15/11/2020 to 15/2/2021 were in Johor (3,129.38%), Kelantan (1,909.95%), and Melaka (1,541.14%), whilst the bottom three were in Labuan (189.04%), Sabah (222.68%), and Kedah (312.02%).

Foreign Workers

The number of foreign workers screened has increased markedly with the government’s mandatory requirement of all foreign workers in the Klang Valley with effect from 1 January, 2021 and throughout the country with effect from 1 February, 2021. 

The foreign workers comprise a significant percentage of the total positive cases, ranging from 35.02% to 41.10% in the period 1 December, 2020 to 15 February, 2021, as shown in Table 2.

It is estimated that there are about two million documented migrant workers comprising about 15% of the total workforce. In addition, the Institute of Migration, an inter-governmental organisation, estimates there are an additional two to four million undocumented workers.

In short, the migrant workers, both documented and undocumented, comprise between 6.25 to 18.75% of the population. This means that migrant workers are between 1.87 to 6.58 times more likely than Malaysians to be tested Covid-19 positive.

As more migrant workers are tested, the cumulative numbers of positives will continue to increase. The prospect of abatement is very slim. This is especially so when the root cause of overcrowding in the accommodation of the migrant workers have yet to be adequately addressed.

While the increase in the cumulative number of positives has been attributed to foreign workers resident in Malaysia, it does not detract from the fact that the rest of the increases of between 58.9-64.9% were in Malaysians.

Case Fatality Ratios

The case fatality ratio (CFR) is the number of deaths divided by identified confirmed cases and multiplied by 100. 

The CFR of the states or territories on 15 November, 2020 and 15 February, 2021 are shown in Table 3. The overall CFR for Malaysia has decreased during this period. This was so for all the states and territories except for Putrajaya and Labuan, both of which recorded increases. 

Tests Are Vital

The MOH’s position six months ago was that the testing capacity then was sufficient. The Deputy Health Minister informed the Dewan Rakyat on 13 August. 2020 that there was no need to waste money and resources to conduct more tests. The 58 laboratories conducting Covid-19 tests then had a testing capacity of up to 38,600 tests daily (Source: Hansard).

Yet on 14 January 2021, the MOH was reported to have instructed home quarantine for all contacts of positive Covid-19 cases and tests only for those who had symptoms.

If less than 50 individuals were exposed in a cluster, then 20 test samples were sufficient.

If the cohort exceeded 50, 30 test samples were enough, or 10% of the cohort, whichever was lower. This was a reflection that the testing capacity was insufficient to meet the needs.

In a media engagement on 5 February 2021, the MOH stated that there were 68 laboratories with a testing capacity of 76,000 and that there were plans to increase the capacity to 200,000 tests daily.

This raises the question of Malaysia’s preparedness for an increase in testing capacity to cope with the increase in the number of cases. It is pertinent to note that China’s daily testing capacity reached 15 million on 27 January 2021, i.e. sufficient for about 1% of its 1.444 billion population.

Be Discriminating

The MOH has been using the term “clusters” to describe the positive cases to date. Cluster is defined in epidemiology as “an aggregation of cases of a disease or another health-related condition closely grouped in time and place.”

The Oxford English dictionary define cluster as “a group of cases of a disease, especially an infectious disease or type of cancer, that occur close together in time or space.”

Some of the “clusters” listed by the MOH describe positive cases found in several states. Is the current usage of the term “cluster” still appropriate?

The World Health Organisation situation report for Malaysia states that there is “large-scale community transmission.”

It is a known fact that the more tests are done, the greater the number of positives will be detected. 

There is daily variation in the number of tests carried out. For example, the number of daily tests varied from 61,483 on 10 February, 2021 to 24,276 on 15 February, 2021. On 9 February, 2021, the MOH stated that only 30% of its testing capacity was utilised the previous day. Yet the number of positives remained high. A high number of positives with relatively fewer tests could only mean that there were many undetected community cases.

The MOH does not disclose the turnaround time for tests. They acknowledged on 31 January, 2021 that there was a backlog of cases dating back to 2020 (i.e. at least a month later), without details on the exact number or how many had been cleared then. The backlog was also attributed to delays in reporting from private health care facilities.

Justin Wolfers, Wharton professor of business and public policy, stated: “Today, consumers of information are drowning in data. Terabytes of data are being generated from the constant measurement of businesses, workers, government and other activity, and there are many ways to draw inferences from the raw data. Unfortunately, many of them lead in the wrong direction.” Does this apply to the Covid-19 data published daily?

Statistical analyses are important tools in evidence-based medicine, but have to be used cautiously and with better understanding. Numerators matter; so do denominators.

Dr Milton Lum is a past President of the Federation of Private Medical Associations, Malaysia and the Malaysian Medical Association. This article is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organisation the writer is associated with.

  • This is the personal opinion of the writer or publication and does not necessarily represent the views of CodeBlue.

 

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